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  • 1.
    Abbas, Ghulam
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Johansson, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Alay-e-Abbas, Syed Muhammad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad 38040, Pakistan.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, J. Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Quasi Three-Dimensional Tetragonal SiC Polymorphs as Efficient Anodes for Sodium-Ion Batteries2023In: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 6, no 17, p. 8976-8988Article in journal (Refereed)
    Abstract [en]

    In the present work, we investigate, for the first time, quasi 3D porous tetragonal silicon–carbon polymorphs t(SiC)12 and t(SiC)20 on the basis of first-principles density functional theory calculations. The structural design of these q3-t(SiC)12 and q3-t(SiC)20 polymorphs follows an intuitive rational approach based on armchair nanotubes of a tetragonal SiC monolayer where C–C and Si–Si bonds are arranged in a paired configuration for retaining a 1:1 ratio of the two elements. Our calculations uncover that q3-t(SiC)12 and q3-t(SiC)20 polymorphs are thermally, dynamically, and mechanically stable with this lattice framework. The results demonstrate that the smaller polymorph q3-t(SiC)12 shows a small band gap (∼0.59 eV), while the larger polymorph of q3-t(SiC)20 displays a Dirac nodal line semimetal. Moreover, the 1D channels are favorable for accommodating Na ions with excellent (>300 mAh g–1) reversible theoretical capacities. Thus confirming potential suitability of the two porous polymorphs with an appropriate average voltage and vanishingly small volume change (<6%) as anodes for Na-ion batteries.

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  • 2.
    Alay-e-Abbas, Syed Muhammad
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Pakistan.
    Abbas, Ghulam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zulfiqar, Waqas
    Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad, 38040, Pakistan; Department of Energy Conversion and Storage, Technical University of Denmark, 2800, Kgs. Lyngby, Denmark.
    Sajjad, Muhammad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Physics, Khalifa University of Science and Technology, Abu Dhabi, 127788, United Arab Emirates.
    Singh, Nirpendra
    Department of Physics, Khalifa University of Science and Technology, Abu Dhabi, 127788, United Arab Emirates; Center for Catalysis and Separation (CeCaS), Khalifa University of Science and Technology, Abu Dhabi, 127788, United Arab Emirates.
    Larsson, J. Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Structure inversion asymmetry enhanced electronic structure and electrical transport in 2D A3SnO (A = Ca, Sr, and Ba) anti-perovskite monolayers2023In: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 16, no 1, p. 1779-1791Article in journal (Refereed)
    Abstract [en]

    Anti-perovskites A3SnO (A = Ca, Sr, and Ba) are an important class of materials due to the emergence of Dirac cones and tiny mass gaps in their band structures originating from an intricate interplay of crystal symmetry, spin-orbit coupling, and band overlap. This provides an exciting playground for modulating their electronic properties in the two-dimensional (2D) limit. Herein, we employ first-principles density functional theory (DFT) calculations by combining dispersion-corrected SCAN + rVV10 and mBJ functionals for a comprehensive side-by-side comparison of the structural, thermodynamic, dynamical, mechanical, electronic, and thermoelectric properties of bulk and monolayer (one unit cell thick) A3SnO anti-perovskites. Our results show that 2D monolayers derived from bulk A3SnO anti-perovskites are structurally and energetically stable. Moreover, Rashba-type splitting in the electronic structure of Ca3SnO and Sr3SnO monolayers is observed owing to strong spin-orbit coupling and inversion asymmetry. On the other hand, monolayer Ba3SnO exhibits Dirac cone at the high-symmetry Γ point due to the domination of band overlap. Based on the predicted electronic transport properties, it is shown that inversion asymmetry plays an essential character such that the monolayers Ca3SnO and Sr3SnO outperform thermoelectric performance of their bulk counterparts.

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  • 3.
    Al-Jayyousi, Hiba
    et al.
    Department of Mechanical Engineering, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates.
    Eswaran, Mathan Kumar
    SRM Research Institute, SRM Institute of Science and Technology, Kattankulathur 603203, Tamil Nadu, India.
    Ray, Avijeet
    Department of Physics, Indian Institute of Technology Roorkee, Roorkee 247667, India.
    Sajjad, Muhammad
    Department of Physics, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates.
    Larsson, J. Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Singh, Nirpendra
    Department of Physics, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates; Center for Catalysis and Separations, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates.
    Exploring the Superior Anchoring Performance of the Two-Dimensional Nanosheets B2C4P2 and B3C2P3 for Lithium-Sulfur Batteries2022In: ACS Omega, E-ISSN 2470-1343, Vol. 7, no 43, p. 38543-38549Article in journal (Refereed)
    Abstract [en]

    Potential anchoring materials in lithium–sulfur batteries help overcome the shuttle effect and achieve long-term cycling stability and high-rate efficiency. The present study investigates the two-dimensional nanosheets B2C4P2 and B3C2P3 by employing density functional theory calculations for their promise as anchoring materials. The nanosheets B2C4P2 and B3C2P3 bind polysulfides with adsorption energies in the range from −2.22 to −0.75 and −2.43 to −0.74 eV, respectively. A significant charge transfer occurs from the polysulfides, varying from −0.74 to −0.02e and −0.55 to −0.02e for B2C4P2 and B3C2P3, respectively. Upon anchoring the polysulfides, the band gap of B3C2P3 reduces, leading to enhanced electrical conductivity of the sulfur cathode. Finally, the calculated barrier energies of B2C4P2 and B3C2P3 for Li2S indicate fast diffusion of Li when recharged. These enthralling characteristics propose that the nanosheets B2C4P2 and B3C2P3 could reduce the shuttle effect in Li–S batteries and significantly improve their cycle performance, suggesting their promise as anchoring materials.

  • 4.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Moriarty, Philip J.
    School of Physics and Astronomy, University of Nottingham.
    Theoretical and Experimental Study of Metal-phthalocyanines on Ag(111).2009Conference paper (Refereed)
    Abstract [en]

    Metal-phthalocyanines deposited and/or self-assembled on metal surface are considered as candidates for novel molecular sensors; molecular memories and photovoltaic cells. To study the adsorption of three metal-phthalocyanines (MPc (M=Co; Sn; Pb) on Ag(111) we performed density functional theory DFT calculations using the generalized gradient approximation (GGA) parameterization by Pedrew-Burke-Ernzerhof (PBE) for the exchange-correlation energy [1;2]. Three initial adsorption site were considered (hcp-hollow; fcc-hollow and on-top). Our results show that the most favourite adsorption site is hcp-hollow for SnPc and PbPc and on-top for CoPc. All calculated structures are compared with experimental data obtained by normal incidence X-ray standing wave spectroscopy (NIXSW) [3;4] Good agreement in binding geometries with experiment was found. To understand the hybridization of MPc s molecular orbitals with silver orbitals we have compared selected partial density of states PDOS for a free and adsorbed MPcs. SnPc and PbPc hybridize mostly with surface by central metal atom; however the effect from the aromatic rings is not negligible. Adsorption of CoPc on the silver surface results in a transfer of electron density from the surface to the central Co atom. After adsorption; the magnetic moment of CoPc is completely quenched which is in agreement with similar studies on adsorption on Au(111) [5]. Binding energies for all of systems are reported showing chemisorptive nature of the molecule-metal surface interaction

  • 5.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Cong, Yan
    School of Physics and Astronomy, University of Nottingham.
    Larsson, Andreas
    Density Functional Study of Metal-Phthalocyanines Interactions With a Silver Surface Ag(111).2007Conference paper (Refereed)
    Abstract [en]

    Metal phthalocyanines (MPc) are generally planar organic molecules comprising of a central metal atom surrounded by aromatic rings. Phthalocyanines are structurally similar to important biomolecules such as haemoglobin and chlorophyll and are commonly used in industry for pigmentation. They have been the focus of intense interest due to their electrical and (non-linear) optical properties. Deposited and/or slef-assembled on metal electrodes, phthalocyanines are attractive candidates for novel molecular sensors, memory, and light-harvesting components. Fundamental understanding of molecule-molecule and molecule-surface interaction is important when attempting to determine the charge transport characteristics of metal phthalocyanines. The most important are the interactions between first layer adsorbate molecules and the substrates, since these interactions determine the structural ordering of the organic films and therefore also have a considerable impact on the efficiency of optical, electronic, and magnetic properties of the system. To study the adsorption of metal-phthalocyanines (MPc (M=Co, Sn, Pb) on the Ag(111) surface we have performed electronic structure calculations using a cluster representation of the surface within the framework of density functional theory (DFT) [1]. Our calculations use the generalized gradient approximation (GGA) parameterization by Pedrew-Burke-Ernzerhof (PBE) for the exchange-correlation energy [2]. We have investigated bonding on three surface adsorption sites (hcp-hollow, fcc-hollow and on-top). SnPc was found to adsorb weakly to the surface, and to prefer hollow bonding rather than on-top bonding. The distance between the Sn atom and the top layer Ag-surface atoms (hcp-hollow and fcc-hollow) is consistent with experimental data obtained by normal incidence X-ray standing wave spectroscopy (NIXSW) [3,4]. Adsorption of CoPc was found very site specific and to prefer the on-top binding site. The distance between the Co atom and the top layer Ag atoms is ~3 . For PbPc, successful adsorption was only obtained on the hcp-hollow site. For SnPc and PbPc binding energy is small fraction of eV, however CoPc bind much strongly to Ag(111) .For each of these systems we have found good agreement in binding geometries with experimental data

  • 6.
    Baran, Jakub D.
    et al.
    School of Chemistry, University of Bath.
    Jarvis, Samuel P.
    School of Physics and Astronomy, University of Nottingham.
    Taylor, Simon
    School of Physics and Astronomy, University of Nottingham.
    Thompson, Damien
    Department of Physics and Energy, Materials and Surface Science Institute, University of Limerick.
    Saywell, Alex
    Fritz Haber Institute of the Max-Planck Society.
    Mangham, Berry
    School of Chemistry, the University of Nottingham.
    Champness, Neil R.
    School of Chemistry, the University of Nottingham.
    Moriarty, Philip
    School of Physics and Astronomy, University of Nottingham.
    Larsson, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    A Case of Unusually Large Density of States Changes For Physisorption - TetraPhenyl-Porphyrins on Cu(111)2015Conference paper (Other academic)
    Abstract [en]

    Conformational changes caused by surface adsorption can dramatically affect a molecule’s properties. The conformational flexibility of the porphyrin family of molecules has been exploited particularly well in a number of contexts, including prototypical molecular switches. Despite this level of study, however, the exact mechanisms underpinning conformational switching are often unclear. We show that the conformation of the tetra(4-bromophenyl) porphyrin (Br4TPP) on Cu(111) depends critically on the precise adsorption site of the molecule, and that, remarkably, large conformational changes are driven entirely by van der Waals (vdW) interactions between the molecule and the substrate surface. A combination of scanning probe microscopy, low temperature single molecule manipulation, dispersion-corrected density functional theory (DFT) and molecular dynamics (MD) simulations shows that van der Waals forces dominate the adsorption of TPP molecules, causing significant distortions of the molecular architecture so that the porphyrin can adopt one of two low energy conformations. In addition, scanning probe manipulation has been used to translate and switch the Br4TPP molecule between conformations via an intermediary, ‘hybrid’ structure. We have used the generalized gradient approximation (GGA) parameterization by Perdew—Burke—Ernzerhof (PBE), and the sparse-matter optBP86b-vdW20 (vdW-DFT) exchange and correlation functional to account for the missing dispersion forces. In order to check for the presence of chemical bonding we have analyzed the molecule-surface complexes using electron localization function (ELF) and Bader charges. We find that vdW-forces alone are capable of causing large shifts in the molecular density of states, despite the complete absence of chemical interactions.

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  • 7.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Kołodziejczyk, Wojciech
    Tyndall National Institute, University College Cork.
    Larsson, Peter O.
    Division of Materials Theory, Department of Physics and Astronomy, Uppsala University.
    Ahuja, Rajeev B.
    Division of Materials Theory, Department of Physics and Astronomy, Uppsala University.
    Larsson, Andreas
    On the stability of single-walled carbon nanotubes and their binding strengths2012In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 131, no 9, p. 1-8Article in journal (Refereed)
    Abstract [en]

    We have studied the relative stability of hydrogen-terminated single-walled carbon nanotubes (SWNTs) segments, and open-ended SWNT fragments of varying diameter and chirality that are present at the interface of the catalytic metal particles during growth. We have found that hydrogen-terminated SWNTs differ by <1 eV in stability among different chiralities, which presents a challenge for selective and property-controlled growth. In addition, both zigzag and armchair tubes can be the most stable chirality of hydrogen-terminated SWNTs, which is a fundamental obstacle for property-controlled growth utilizing thermodynamic stability. In contrast, the most armchair-like open-ended SWNTs segments are always the most stable ones, followed in sequence by chiral index up to the least stable zigzag segments. We explain the ordering by triple bond stabilization of the carbon dangling bonds at the open ends, which is a fragment stabilization effect that is only manifested when all bonds between two layers are broken. We show convincingly that the bond strength difference between zigzag and armchair tubes is not present when individual bonds are broken or formed

  • 8.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    A DFT study employing dispersion correction of adsorption of SnPc and CoPc on the Ag(111) surface2011Conference paper (Refereed)
  • 9. Baran, Jakub D.
    et al.
    Larsson, Andreas
    Adsorption Of Metal-Phthalocyanines on Ag(111): A First-Principles Study2008Conference paper (Refereed)
  • 10.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    DFT Computations of Metal Phthalocyanies on Ag(111)2008Conference paper (Refereed)
  • 11.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Structure and energetics of shuttlecock-shaped tin-phthalocyanine on Ag(111: A density functional study employing dispersion correction2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, p. 9487-9497Article in journal (Refereed)
    Abstract [en]

    The reversible switch between two electronically and/or geometrically distinct states of a single molecule adsorbed on a well-characterized substrate is of high technological interest due to its possible use as single molecule devices and novel molecular memories. We have studied shuttlecock-shaped metal phthalocyanines, which can adsorb on surfaces in two distinct adsorption configurations, depending on if the central metal atom points toward or away from the surface, and we report on the adsorption of tin-phthalocyanine (SnPc) on an Ag(111) surface using density functional theory (DFT) including a semiempirical dispersion correction (DFT-D).We discuss the binding mechanism in detail and show that the adsorption of SnPc in these two orientations is driven by very different interactions. While "Sn-down" adsorption involves chemical bonding between Sn and the surface (chemisorption), the "Sn-up" configuration is bound only by weak van der Waals forces (physisorption). By comparing our theoretical results with a broad range of experimental data, we assess the effect of dispersion forces for the SnPc/Ag(111) system and how these impact adsorption energies, geometries, and the electronic structure. We show that an inclusion of dispersion forces improves the adsorption geometry with respect to experiment and is essential in order to capture the subtle electronic effects at molecule-metal interfaces. By analyzing the geometric and electronic structure of the adsorbed molecules we, in addition, shed light on the surprising 2-fold symmetry reduction of metal phthalocyanine molecules that has been observed upon adsorption on surfaces

  • 12.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Theoretical insights into adsorption of cobalt phthalocyanine on Ag(111): A combination of chemical and van der Waals bonding2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 45, p. 23887-23898Article in journal (Refereed)
    Abstract [en]

    In this article we study in detail the interaction of cobalt phthalocyanine (CoPc) with the Ag(111) surface by means of density functional theory calculations (DFT). We discuss the electronic and geometric differences of the adsorbed CoPc as it interacts with the different binding sites of the surface, yielding deeper insight into the adsorption mechanism of organometallic molecules with noble metal surfaces. We interpret the experimentally observed 4-fold to 2-fold symmetry reduction upon interaction of phthalocyanine molecules with metal surfaces as caused by electronic effects originating from nonsymmetric interactions between the molecule and the surface. To asses the role of dispersion forces in bonding of CoPc to the surface we employ a semiempirical dispersion correction to standard DFT and compare the obtained molecule-surface separation with experimental measurements. We show that, in the case of CoPc, the molecule bonds to the surface mostly due to covalent bonding between Co and Ag, but with a considerable contribution from van der Waals bonding between the Pc ligand and the surface. We show in this case where the molecule-surface separation is mostly governed by covalent bonding between the central metal atom and the surface atoms that standard DFT performs reasonably well, as compared to the available experimental data.

  • 13.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Theoretical Study Of Metal-Phthalocyanies MPc (M=Co; Sn; Pb) With Silver Surface Ag(111) And Reversible Conformational Inversion2008Conference paper (Refereed)
    Abstract [en]

    Metal-phthalocyanie adsorbed on metal surfaces are class of materials particularly promising as a building blocks for molecular electronic devices. Their application rely on the electrochemically induced switching of their electronic and magnetic state has been demonstrated [1]. The knowledge of their molecular geometry and electronic structure as a single entities and when adsorbed on surface are crucial points in order to understand their interaction with surfaces. By means of density functional theory (DFT) we have investigated conformational interconversion ( see Fig. 1) of single MPc molecules as their interaction with Ag(111) silver surfaces. Structural analysis using B3-LYP functional; and DZVP2 and TZVPP2 [2] basis set has been performed to evaluate the transition state (TS) and energy barrier of this conversion. We have found two different mechanism of inversion for SnPc and PbPc. To study the adsorption of metal-phthalocyanies MPc (M=Co; Sn; Pb) bonded parallel to the Ag(111) surface we used cluster representation of surface (55 and 169 silver atoms). To perform this calculations the generalized gradient approximation (GGA) parameterisation by Pedrew-Burke-Ernzerhof (PBE) for exchange-correlation energy [3] and multipole resolution of identity [4] method were used. We have investigated bonding on three surface adsorption sites (hcp-hollow; fcc-hollow and on-top). For each of these systems we have found good agreement in binding geometries with experimental data obtained by normal incidence X-ray standing wave spectroscopy (NIXSW) [4;5]. Binding energies and geometries for all systems are given. We have used electronic structure calculations to better understand these molecules as a separate entities and as a devices

  • 14.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Cong, Yan
    School of Physics and Astronomy, University of Nottingham.
    Interactions of Metal-phthalocyanines MPc (M=Co; Sn; Pb) with Silver Surface Ag(111)2007Conference paper (Refereed)
  • 15.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Cong, Yan
    School of Physics and Astronomy, University of Nottingham.
    Moriarty, Philip J.
    School of Physics and Astronomy, University of Nottingham.
    DFT Computation Of Metal-Phthalocyanines Bonded To Ag(111)2007Conference paper (Refereed)
    Abstract [en]

    To study the adsorption of metal-phthalocyanines (MPc (M=Co; Sn; Pb) on the Ag(111) surface we have performed electronic structure calculations using a cluster representation of the surface within the framework of density functional theory (DFT) [1]. Our calculations use the generalized gradient approximation (GGA) parameterization by Pedrew-Burke-Ernzerhof (PBE) for the exchange-correlation energy [2]. We have investigated bonding on three surface adsorption sites (hcp-hollow; fcc-hollow and on-top). SnPc was found to adsorb weakly to the surface (0.15 to 0.25 eV); and to prefer hollow bonding rather than on-top bonding. The distance between the Sn atom and the top layer Ag-surface atoms (hcp-hollow and fcc-hollow) is consistent with experimental data obtained by normal incidence X-ray standing wave spectroscopy (NIXSW) [3;4]. CoPc is much more strongly bound to the Ag(111) surface and was found to prefer the on-top site. The calculated binding energy is 1.2 eV and the distance between the Co atom and the top layer Ag atoms is 3 (which also matched the experimental data well). For PbPc; successful adsorption was only obtained on the hcp-hollow site with a binding energy of 0.5 eV. For each of these systems we have found good agreement in binding geometries with experimental data.

  • 16.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Cong, Yan
    School of Physics and Astronomy, University of Nottingham.
    Moriarty, Philip J.
    School of Physics and Astronomy, University of Nottingham.
    Interactions of Metal-phthalocyanines MPc (M=Co; Sn; Pb) with Silver Surface Ag(111): A Density Functional Study2008Conference paper (Refereed)
    Abstract [en]

    Deposited and/or self-assembled on metal electrodes; metal-phthalocyanine are attractive candidates for novel molecular sensors; memory; and light-harvesting components. The knowledge of the their molecular geometry and electronic structure are crucial points in order to understand their interactions with surfaces. To study the adsorption of metal-phthalocyanines (MPc (M=Co; Sn; Pb) bonded parallel on the Ag(111) surface we have performed electronic structure calculations using a cluster representation (55 and 169 silver atoms) of the surface within the framework of density functional theory (DFT) [1]. Our calculations use the generalized gradient approximation (GGA) parameterization by Pedrew-Burke-Ernzerhof (PBE) for the exchange-correlation energy [2] and multipole accelerated resolution of identity method [3]. We have investigated bonding on three surface adsorption sites (hcp-hollow; fcc-hollow and on-top). For each of these systems we have found good agreement in binding geometries with experimental data obtained by normal incidence X-ray standing wave spectroscopy (NIXSW) [4;5]. Binding energies and geometries for all systems are given. We propose flat chemisorption of respective MPcs on Ag(111).

  • 17.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    cong, Yan
    School of Physics and Astronomy, University of Nottingham.
    Moriarty, Philiph J.
    School of Physics and Astronomy, University of Nottingham.
    Interactions of Metal-phthalocyanines with Silver Surface Ag(111: A Density Functional Theory Study2008Conference paper (Refereed)
  • 18.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Woolley, Richard A.J-
    School of Physics and Astronomy, University of Nottingham.
    Cong, Yan
    School of Physics and Astronomy, University of Nottingham.
    Moriarty, Philip J.
    School of Physics and Astronomy, University of Nottingham.
    Cafolla, Attilio Anthony
    School of Physics and Astronomy, University of Nottingham.
    Schulte, Karina H.G.
    MAX-lab, Lund University.
    Dhanak, Vinod R.
    Department of Physics, University of Liverpool.
    Theoretical and experimental comparison of SnPc, PbPc, and CoPc adsorption on Ag(111)2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 7Article in journal (Refereed)
    Abstract [en]

    A combination of normal-incidence x-ray standing-wave (NIXSW) spectroscopy, x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and density-functional theory (DFT) has been used to investigate the interaction of a number of phthalocyanine molecules (specifically, SnPc, PbPc, and CoPc) with the Ag(111) surface. The metal-surface distances predicted by the DFT calculations for SnPc/Ag(111) (2.48Å) and CoPc/Ag(111) (2.88Å) are in good agreement with our NIXSW experimental results for these systems (2.31±0.09 and 2.90±0.05Å, respectively). Good agreement is also found between calculated partial density-of-states plots and STM images of CoPc on Ag(111). Although the DFT and Pb4f NIXSW results for the Pb-Ag(111) distance are similarly in apparently good agreement, the Pb4f core-level data suggest that a chemical reaction between PbPc and Ag(111) occurs due to the annealing procedure used in our experiments and that the similarity of the DFT and Pb4f NIXSW values for the Pb-Ag(111) distance is likely to be fortuitous. We interpret the Pb4f XPS data as indicating that the Pb atom can detach from the PbPc molecule when it is adsorbed in the "Pb-down" position, leading to the formation of a Pb-Ag alloy and the concomitant reduction in Pb from a Pb2 + state (in bulklike films of PbPc) to Pb0. In contrast to SnPc, neither PbPc nor CoPc forms a well-ordered monolayer on Ag(111) via the deposition and annealing procedures we have used. Our DFT calculations show that each of the phthalocyanine molecules donate charge to the silver surface, and that back donation from Ag to the metal atom (Co, Sn, or Pb) is only significant for CoPc

  • 19.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork, Cork, Lee Maltings Prospect Row, Ireland.
    Larsson, J. Andreas
    Tyndall National Institute, University College Cork, Cork, Lee Maltings Prospect Row, Ireland.
    Inversion of the shuttlecock shaped metal phthalocyanines MPc (M = Ge, Sn, Pb) - A density functional study2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 23, p. 6179-6186Article in journal (Refereed)
  • 20.
    Batool, Javaria
    et al.
    Computational Materials Modeling Laboratory, Department of Physics, Government College University Faisalabad, 38040 Faisalabad, Pakistan; Department of Physics, Government College Women University Faisalabad, Faisalabad, Pakistan.
    Alay-e-Abbas, Syed Muhammad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Computational Materials Modeling Laboratory, Department of Physics, Government College University Faisalabad, 38040 Faisalabad, Pakistan.
    Johansson, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zulfiqar, Waqas
    Computational Materials Modeling Laboratory, Department of Physics, Government College University Faisalabad, 38040 Faisalabad, Pakistan.
    Danish, Muhammad Arsam
    Computational Materials Modeling Laboratory, Department of Physics, Government College University Faisalabad, 38040 Faisalabad, Pakistan.
    Bilal, Muhammad
    Computational Materials Modeling Laboratory, Department of Physics, Government College University Faisalabad, 38040 Faisalabad, Pakistan.
    Larsson, J. Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Amin, Nasir
    Computational Materials Modeling Laboratory, Department of Physics, Government College University Faisalabad, 38040 Faisalabad, Pakistan.
    Oxygen-vacancy-induced magnetism in anti-perovskite topological Dirac semimetal Ba3SnO2021In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 23, no 43, p. 24878-24891Article in journal (Refereed)
    Abstract [en]

    The thermodynamic, structural, magnetic and electronic properties of the pristine and intrinsic vacancy-defect-containing topological Dirac semimetal Ba3SnO are studied using first-principles density functional theory calculations. The thermodynamic stability of Ba3SnO has been evaluated with reference to its competing binary phases Ba2Sn, BaSn and BaO. Subsequently, valid limits of the atomic chemical potentials derived from the thermodynamic stability were used for assessing the formation of Ba, Sn and O vacancy defects in Ba3SnO under different synthesis environments. Based on the calculated defect-formation energies, we find that the charge-neutral oxygen vacancies are the most favourable type of vacancy defect under most chemical environments. The calculated electronic properties of pristine Ba3SnO show that inclusion of spin–orbit coupling in exchange–correlation potentials computed using generalized gradient approximation yields a semimetallic band structure exhibiting twin Dirac cones along the Γ–X path of the Brillouin zone. The effect of spin–polarization and spin–orbit coupling on the physical properties of intrinsic vacancy defects containing Ba3SnO has been examined in detail. Using Bader charges, electron localization function (ELF), electronic density of states (DOS) and spin density, we show that the isolated oxygen vacancy is a magnetic defect in anti-perovskite Ba3SnO. Our results show that the origin of magnetism in Ba3SnO is the accumulation of unpaired charges at the oxygen vacancy sites, which couple strongly with the 5d states of the Ba atom. Owing to the metastability observed in earlier theoretically predicted magnetic topological semimetals, the present study reveals the important role of intrinsic vacancy defects in giving rise to magnetism and also provides opportunities for engineering the electronic structure of a Dirac semimetal.

  • 21. Beton, P.
    et al.
    Moriarty, P.
    Keeling, D.
    Dunsch, L.
    Georgi, P.
    Wang, Chun-Ru
    Greer, J.C.
    Larsson, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Smith, R.
    Godwin, P.
    Suter, D.
    Udovicic, L.
    Weidinger, A.
    Harneit, W.
    Waiblinger, M.
    Welland, M.
    Durkan, C.
    A study for the construction of a quantum information precessing device using doped fullerenes2000Conference paper (Refereed)
  • 22.
    Bolton, Kim
    et al.
    Physics Department, Göteborg University.
    Larsson, Peter
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Larsson, Andreas
    Aruja, Rajeev B.
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Ding, Feng
    Physics Department, Göteborg University.
    Duan, HaiMing
    Physics Department, Göteborg University.
    Rosén, Arne E.
    Physics Department, Göteborg University.
    Börjesson, A.
    Harutyunyan, A.R.
    Mora, E.
    Tokune, T.
    Jiang, A.
    Awasthi, N.
    Setyawan, W.
    Curtarolo, S.
    Computational Modeling of SWNTs and Their Growth2007Conference paper (Refereed)
  • 23.
    Bolton, Kim
    et al.
    Physics Department, Göteborg University.
    Larsson, Peter O.
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Larsson, Andreas
    Ahuja, Rajeev B.
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Ding, Feng
    Physics Department, Göteborg University.
    Duan, HaiWing
    Physics Department, Göteborg University.
    Zhu, W.
    Börjesson, A.
    Harutyunyan, H.R.
    Tokune, T.
    Curtarolo, S
    Carbon Nanotube Growth Mechanisms2007In: Proceedings of Diamond 2007, the 18th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide: [... (Diamond 2007), Berlin, Germany, 10-14 September 2007], 2007Conference paper (Refereed)
    Abstract [en]

    We have used a variety of computational methods to study key aspects of single-walled carbon nanotube (SWNT) growth. Molecular dynamics (MD) studies based on an empirical force field showed; for example; why SWNT growth occurs in a temperature window and why; for 1-2 nm catalyst particles; the SWNT diameter varies linearly with the size of the particle. In addition; the liquid or solid phase of the catalyst particle is strongly dependent on particle size; and smaller particles (< 1.5 nm) are liquid at typical chemical vapor deposition temperatures whereas larger particles (> 5 nm) are solid. The phase of particles of intermediate sizes depends on the exact temperature and on their carbon content. The effect of substrates on metal-carbide properties and SWNT growth has been studied by combing density functional (DFT) and MD methods. A major effect of flat; inert substrates is to flatten the catalyst particles thereby increasing their melting points. DFT has also been used to study the catalyst-SWNT interaction which is critical for the growth of long SWNTs; and is also being used to study the importance of the SWNT cap structure on its chirality. This knowledge is important; for example; when using SWNTs as seeds for the growth of longer nanotubes.

  • 24.
    Christen, Dines
    et al.
    Institut für Physikalische und Theoretische Chemie, Universität Tübingen, D-72076, Tübingen, Auf der Morgenstelle 8, Germany.
    Coudert, Laurent H.
    Laboratoire de Photophysique Moléculaire, CNRS, Université de Paris-Sud, 91405, Orsay Cedex, Bâtiment 210, France.
    Larsson, Andreas
    Department of Theoretical Chemistry, Göteborg Univearsity, SE-41320, Göteborg, Reutersgatan 2, Sweden.
    Cremer, Dieter
    Department of Theoretical Chemistry, Göteborg Univearsity, SE-41320, Göteborg, Reutersgatan 2, Sweden.
    The rotational-torsional spectrum of the g′Gg conformer of ethylene glycol: Elucidation of an unusual tunneling path2001In: Journal of Molecular Spectroscopy, ISSN 0022-2852, E-ISSN 1096-083X, Vol. 205, no 2, p. 185-196Article in journal (Refereed)
  • 25. Cremer, Dieter
    et al.
    Larsson, Andreas
    Kraka, Elif
    Department of Theoretical Chemistry, Göteborg University.
    New developments in the analysis of vibrational spectra On the use of adiabatic internal vibrational modes1998In: Theoretical and Computational Chemistry, ISSN 1380-7323, Vol. 5, no C, p. 259-327Article in journal (Refereed)
  • 26.
    Cremer, Dieter
    et al.
    Department of Theoretical Chemistry, Göteborg University.
    Wu, A.N.
    Department of Theoretical Chemistry, Göteborg University.
    Larsson, Andreas
    Kraka, Elif
    Department of Theoretical Chemistry, Göteborg University.
    Some thoughts about bond energies, bond lengths, and force constants2000In: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 6, no 4, p. 396-412Article in journal (Refereed)
    Abstract [en]

    The bond energy (BE) of a polyatomic molecule cannot be measured and, therefore, determination of BEs can only be done within a model using a set of assumptions. The bond strength is reflected by the intrinsic BE (IBE), which is related to the intrinsic atomization energy (IAE) and which represents the energy of dissociation under the provision that the degree of hybridization is maintained for all atoms of the molecule. IBE and BE differ in the case of CC and CH bonds by the promotion, the hybridization, and the charge reorganization energy of carbon. Since the latter terms differ from molecule to molecule, IBE and BE are not necessarily parallel and the use of BEs from thermochemical models can be misleading. The stretching force constant is a dynamical quantity and, therefore, it is related to the bond dissociation energy (BDE). Calculation and interpretation of stretching force constants for local internal coordinate modes are discussed and it is demonstrated that the best relationship between BDEs and stretching force constants is obtained within the model of adiabatic internal modes. The valence stretching force constants are less suitable since they are related to an artificial bond dissociation process with geometrical relaxation effects suppressed, which leads to an intrinsic BDE (IBDE). In the case of AX(n) molecules, symmetric coordinates can be used to get an appropriate stretching force constant that is related to the BE. However, in general stretching force constants determined for symmetry coordinates do not reflect the strength of a particular bond since the related dissociation processes are strongly influenced by the stability of the products formed.

  • 27.
    Delaney, Paul
    et al.
    Queen's University Belfast.
    Larsson, Andreas
    Greer, James C.
    Tyndall National Institute, University College Cork.
    Singlet and Triplet Levels of the NV Centre2011Conference paper (Refereed)
  • 28.
    Delaney, Paul
    et al.
    Queen's University Belfast, Belfast, BT7 1NN, Northern Ireland, University Road, United Kingdom.
    Greer, James C.
    Tyndall National Institute, University College Cork, Lee Maltings, Cork, Prospect Row, Ireland.
    Larsson, J. Andreas
    Tyndall National Institute, University College Cork, Lee Maltings, Cork, Prospect Row, Ireland.
    Spin-polarization mechanisms of the nitrogen-vacancy center in diamond2010In: Nano Letters, ISSN 1530-6984, E-ISSN 1530-6992, Vol. 10, no 2, p. 610-614Article in journal (Refereed)
  • 29.
    Delaney, Paul
    et al.
    Queen's University Belfast.
    Larsson, Andreas
    Small cluster model of the NV centre in diamond2010In: Physics Procedia, E-ISSN 1875-3892, Vol. 3, no 4, p. 1533-1537Article in journal (Refereed)
    Abstract [en]

    The singlet 1E and 1A 1 energy levels of the Nitrogen-Vacancy centre's ground state configuration each need two Slater determinants in theoretical models, posing difficulties for Density-Functional Theory (DFT) and Hartree-Fock approaches. Configuration Interaction (CI) can handle such states, but not the C 284H 144N - and C 163H 100N - clusters of our recent DFT study as CI computer time and memory scale worse than DFT with system size. Using smaller clusters to model bulk diamond introduces size errors. We examine the smaller diamond cluster C 42H 42N - using DFT to quantify the size error: if not too large it opens the way to CI calculations of these states.

  • 30.
    Ding, Feng
    et al.
    Physics Department, Göteborg University.
    Larsson, Oeter
    Department of Physics, University of Uppsala.
    Larsson, Andreas
    Ahuja, Rajeev
    Department of Physics, University of Uppsala.
    Duan, Haiming
    Physics Department, Göteborg University.
    Rosén, Arne
    Physics Department, Göteborg University.
    Bolton, Kim
    Physics Department, Göteborg University.
    Strong SWNT-catalyst adhesion strength as a necessary condition for SWNT growth2007Conference paper (Refereed)
  • 31.
    Ding, Feng
    et al.
    Physics Department, Göteborg University.
    Larsson, Peter O.
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Ahuja, Rajeev B.
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Larsson, Andreas
    Duan, HaiMing
    Physics Department, Göteborg University.
    Rosén, Arne E.
    Physics Department, Göteborg University.
    Bolton, Kim
    Physics Department, Göteborg University.
    The Importance of Metal particle: Nanotube Binding for Single Walled Nanotube Growth2006Conference paper (Refereed)
  • 32.
    Ding, Feng
    et al.
    Physics Department, Göteborg University.
    Larsson, Peter O.
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Larsson, Andreas
    Ahuja, Rajeev B.
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Duan, HaiMing
    Physics Department, Göteborg University.
    Rosen, Arne E.
    Physics Department, Göteborg University.
    Bolton, Kim
    Physics Department, Göteborg University.
    The importance of strong carbon-metal adhesion for catalytic nucleation of single-walled carbon nanotubes2008In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, no 2, p. 463-468Article in journal (Refereed)
    Abstract [en]

    Density functional theory is used to show that the adhesion between single-walled carbon nanotubes (SWNTs) and the catalyst particles from which they grow needs to be strong to support nanotube growth. It is found that Fe, Co, and Ni, commonly used to catalyze SWNT growth, have larger adhesion strengths to SWNTs than Cu, Pd, and Au and are therefore likely to be more efficient for supporting growth. The calculations also show that to maintain an open end of the SWNT it is necessary that the SWNT adhesion strength to the metal particle is comparable to the cap formation energy of the SWNT end. This implies that the difference between continued and discontinued SWNT growth to a large extent depends on the carbon-metal binding strength, which we demonstrate by molecular dynamics (MD) simulations. The results highlight that first principles computations are vital for the understanding of the binding strength's role in the SWNT growth mechanism and are needed to get accurate force field parameters for MD

  • 33.
    Fadaei Naeini, Vahid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Unraveling the pressure-viscosity behavior and shear thinning in glycerol using atomic scale molecular dynamics simulations2023In: Journal of Molecular Liquids, ISSN 0167-7322, E-ISSN 1873-3166, Vol. 390, no part A, article id 122990Article in journal (Refereed)
    Abstract [en]

    In order to increase the usage and explore new applications of glycerol as a replacement for fossil-based lubricants its properties needs to be known at the fundamental level. In this study, the viscosity of pure glycerol at high pressures and strain rates has been investigated using of molecular dynamics (MD) simulations, utilizing both the Green-Kubo (GK) formalism and the SLLOD algorithm. Although the viscosity acquired by the GK method is in agreement with the corresponding experimental values at low pressure, a significant distinction was identified between the viscosity obtained by the GK method and the experimental values at higher pressures (P > 0.5 GPa). This results in a clear difference between the viscosity-pressure coefficient attained by the GK method and the corresponding experimental value. The SLLOD method using a non-equilibrium MD (NEMD) platform was exploited to take into account the simultaneous effects of strain rate and pressure on viscosity. As a result, the pressure-viscosity coefficient acquired by the SLLOD algorithm approaches the experimental value. By combining the experimental outputs for viscosity at low strain rates ( < 104 s−1) with the SLLOD outputs at higher rates ( > 105 s−1), the evolutions of glycerol viscosity with pressure and strain rate were ultimately achieved. Implementing this computational platform depicts the shear thinning process in pure glycerol in a wide range of pressures and strain rates.

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  • 34.
    Fransson, Jonas
    et al.
    Department of Materials Science and Engineering, Royal Institute of Technology.
    Bengone, Oliver M.
    Department of Physical Electronic/Photonic, Mitthögskolan.
    Larsson, Andreas
    Greer, James C.
    Tyndall National Institute, University College Cork.
    A physical compact model for electron transport across single molecules2006In: IEEE transactions on nanotechnology, ISSN 1536-125X, E-ISSN 1941-0085, Vol. 5, no 6, p. 745-749Article in journal (Refereed)
    Abstract [en]

    Prediction of current flow across single molecules requires ab initio electronic structure calculations along with their associated high computational demand, and a means for incorporating open system boundary conditions to describe the voltage sources driving the current. To date, first principle predictions of electron transport across single molecules have not fully achieved a predictive capability. The situation for molecular electronics may be compared to conventional technology computer-aided design (TCAD), whereby various approximations to the Boltzmann transport equation are solved to predict electronic device behavior, but in practice are too time consuming for most circuit design applications. To simplify device models for circuit design, analytical but physically motivated models are introduced to capture the behavior of active and passive devices; however, similar models do not yet exist for molecular electronics. We follow a similar approach by evaluating an analytical model achieved by combining a mesoscopic transport model with parameterizations taken from quantum chemical calculations of the electronic structure of single molecule bonded between two metal contacts. Using the model to describe electron transport across benzene-1,4-dithiol and by comparing to experiment, we are able to extract the coupling strength of the molecule attached to two infinite metal electrodes. The resulting procedure allows for accurate and computationally efficient modeling of the static (dc) characteristics of a single molecule, with the added capability of being able to study the physical model parameter variations across a range of experiments. Such simple physical models are also an important step towards developing a design methodology for molecular electronics

  • 35.
    Gannon, Greg
    et al.
    Tyndall National Institute, University College Cork, Cork, Ireland.
    Greer, James C.
    Tyndall National Institute, University College Cork, Cork, Ireland.
    Larsson, J. Andreas
    Tyndall National Institute, University College Cork, Cork, Ireland.
    Thompson, Damien J.
    Tyndall National Institute, University College Cork, Cork, Ireland.
    Molecular dynamics study of naturally occurring defects in self-assembled monolayer formation2010In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 4, no 2, p. 921-932Article in journal (Refereed)
  • 36.
    Gannon, Greg
    et al.
    Tyndall National Institute, Lee Makings, Prospect Row, Cork.
    Larsson, Andreas
    Greer, James C.
    Tyndall National Institute, Lee Makings, Prospect Row, Cork.
    Thompson, Damien J.
    Tyndall National Institute, Lee Makings, Prospect Row, Cork.
    Modelling ink spreading on self-assembled monolayers for nanopatterning applications2008Conference paper (Refereed)
    Abstract [en]

    Alkanethiol self-assembled monolayers (SAMs) on gold; specifically the Au(111) surface; have been widely studied since their discovery in the early 1980 s. The interest in SAMs is due in part to their ease of production but also due to their present and potential application in technologies as diverse as biosensors; corrosion protection and nanolithography. Spreading of ink outside the desired printed area is one of the major limitations of microcontact printing (m-CP) with alkanethiol self-assembled monolayers (SAMs) on gold.1;2 We use molecular dynamics (MD) computer simulations to quantify the temperature and concentration dependence of hexadecanethiol (HDT) ink spreading on HDT SAMs; modelling 18 distinct printing conditions using periodic simulation cells of ~7 nm edge length and printing conditions ranging from 7 ink molecules per cell at 270 K to 42 ink molecules per cell at 371K.3 The computed alkanethiol ink diffusion rates on the SAM are of the same order of magnitude as bulk liquid alkanethiol diffusion rates at all but the lowest ink concentrations and highest temperatures; with up to 20-30 times increases in diffusion rates at the lowest concentration-highest temperature conditions. We show that although alkanethiol surfaces are autophobic; autophobicity is not enough to pin the ink solutions on the SAM and so any over-inking of the SAM will lead to spreading of the printed pattern. Comparison of experimental and calculated diffusion data supports an interpretation of pattern broadening as a mixture of spreading on fully- and partially-formed SAMs; and the calculated spreading rates establish some of the fundamental limitations of m-CP in terms of stamp contact time and desired pattern width

  • 37.
    Gannon, Greg
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Thompson, Damien J.
    Tyndall National Institute, University College Cork.
    Monolayer packing, dehydration, and ink-binding dynamics at the molecular2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 17, p. 7298-7304Article in journal (Refereed)
    Abstract [en]

    Gold-bound self-assembled monolayers (SAMs) terminating in β-cyclodextrin (β-CD) cavities provide a highly ordered surface array of hydrophobic binding pockets and so are used as "molecular printboards" for nanopatterning applications. The present work complements ongoing nanoscale experiments by providing the atom-scale structure, dynamics, and energetics of the printboard, which may aid the design of functional platforms for nanotechnology. We use fully atomistic molecular dynamics (MD) computer simulations to probe the printboard lattice constant, height, steric packing, hydrophobicity, and ink-binding properties as a function of gold-β-CD "linker" molecule and degree of binding to gold. The simulations reveal the stabilization associated with the experimentally observed surface lattice constant of ∼2 nm, alkanethioether linkers, and partial unbinding from gold. Additional ink-binding simulations indicate that multivalent ink molecules can offset disordering in the more loosely packed alkanethiol-linked printboard, with the attendant steric penalty similar in magnitude to the favorable multivalent ink:β-CD complexation

  • 38.
    Gannon, Greg
    et al.
    Tyndall National Institute, Cork, Lee Maltings, Prospect Row, Ireland.
    Larsson, J. Andreas
    Tyndall National Institute, Cork, Lee Maltings, Prospect Row, Ireland.
    Greer, James C.
    Tyndall National Institute, Cork, Lee Maltings, Prospect Row, Ireland.
    Thompson, Damien
    Tyndall National Institute, Cork, Lee Maltings, Prospect Row, Ireland.
    Guanidinium chloride molecular diffusion in aqueous and mixed water-ethanol solutions2008In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 112, no 30, p. 8906-8911Article in journal (Refereed)
  • 39.
    Gannon, Greg
    et al.
    Tyndall National Institute, Lee Makings, Cork, Prospect Row, Ireland.
    Larsson, J. Andreas
    Tyndall National Institute, Lee Makings, Cork, Prospect Row, Ireland.
    Greer, James C.
    Tyndall National Institute, Lee Makings, Cork, Prospect Row, Ireland.
    Thompson, Damien
    Tyndall National Institute, Lee Makings, Cork, Prospect Row, Ireland.
    Quantification of ink diffusion in microcontact printing with self-assembled monolayers2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 1, p. 242-247Article in journal (Refereed)
  • 40.
    Gannon, Greg
    et al.
    Theory Modelling and Design Centre, Tyndall National Institute, University College Cork, Cork, Ireland; Laboratory of Computational Chemistry and Biochemistry, Departement für Chemie and Biochemie, Universität Bern, CH-3012 Bern, Freiestrasse 3, Switzerland.
    O'Dwyer, Colm
    Department of Physics and Energy, Materials and Surface Science Institute, University of Limerick, Limerick, Ireland.
    Larsson, J. Andreas
    Theory Modelling and Design Centre, Tyndall National Institute, University College Cork, Cork, Ireland.
    Thompson, Damien
    Theory Modelling and Design Centre, Tyndall National Institute, University College Cork, Cork, Ireland.
    Interdigitating organic bilayers direct the short interlayer spacing in hybrid organic-inorganic layered vanadium oxide nanostructures2011In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 115, no 49, p. 14518-14525Article in journal (Refereed)
  • 41.
    Gannon, Greg
    et al.
    Tyndall National Institute, University College Cork.
    Thompson, Damien J.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Greer, James C.
    Tyndall National Institute, University College Cork.
    A Molecular dynamics study of alkanoethiol diffusion on alkanethiol self-assembled monolayers2007Conference paper (Refereed)
  • 42.
    Gannon, Greg
    et al.
    Tyndall National Institute, University College Cork.
    Thompson, Damien J.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Greer, James C.
    Tyndall National Institute, University College Cork.
    Atomistic simulations of nanopatterning systems2006Conference paper (Refereed)
  • 43.
    Gannon, Greg
    et al.
    Tyndall National Institute, University College Cork.
    Thompson, Damien J.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Greer, James C.
    Tyndall National Institute, University College Cork.
    Computational study of self-assembled monolayers of thiolates and hepththioether functionalized Beta-cyclodextrins on a Au(III) surface2005Conference paper (Refereed)
  • 44.
    Gannon, Greg
    et al.
    Tyndall National Institute, University College Cork.
    Thompson, Damien J.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Greer, James C.
    Tyndall National Institute, University College Cork.
    Molecular dynamics simulations of self-assembled monolayers for nanopatterning applications2007Conference paper (Refereed)
    Abstract [en]

    Self-Assembled Monolayers (SAMs) are used in areas as diverse as corrosion protection; nanodevices and biotechnology. Despite a wealth of both experimental and theoretical studies of SAM structure and behaviour[1]; there still remain some unanswered questions. Alkanethiol molecular ink diffusion on alkanethiol SAMs is one such area; and one amenable to computational study. Ink diffusion is an important consideration when one performs microcontact printing - "... the quality of the printed pattern strongly depends on the mobility of the ink compound ..."[2]. An understanding of ink diffusion is therefore crucial to the production of stable; high-resolution nanopatterns. We first of all calculated alkanethiol self-diffusion coefficients in bulk liquid and obtained good agreement with measured values. The Einstein diffusion equation was used to calculate the diffusion coefficients from 1 nanosecond molecular dynamics (MD) simulations Simulations of alkanethiol SAMs were performed and the temperature dependence of the SAM tilt angle found to be in good agreement with literature values. Having validated our method both for calculating diffusion and the SAM structural models; we calculated the diffusion of both a single alkanethiol molecule and a 75-molecule drop ; on a range of perfect and defect SAMs; establishing a range for ink diffusion in different environments and; ultimately; allowing identification of optimum ink molecular weights for microcontact printing applications

  • 45.
    Han, Sang Sub
    et al.
    NanoScience Technology Center, University of Central Florida, Orlando, Florida 32826, United States; Department of Materials Science and Engineering, Seoul National University, Seoul 08826, South Korea.
    Ko, Tae-Jun
    NanoScience Technology Center, University of Central Florida, Orlando, Florida 32826, United States.
    Shawkat, Mashiyat Sumaiya
    NanoScience Technology Center, University of Central Florida, Orlando, Florida 32826, United States; Department of Electrical and Computer Engineering, University of Central Florida, Orlando, Florida 32826, United States.
    Shum, Alex Ka
    Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, Florida 32826, United States.
    Bae, Tae-Sung
    Analytical Research Division, Korea Basic Science Institute, Jeonju 54907, South Korea.
    Chung, Hee-Suk
    Analytical Research Division, Korea Basic Science Institute, Jeonju 54907, South Korea.
    Ma, Jinwoo
    Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27606, United States.
    Sattar, Shahid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Physics and Electrical Engineering, Linnaeus University, SE-39231 Kalmar, Sweden.
    Hafiz, Shihab Bin
    Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, New Jersey 07102, United States.
    Mahfuz, Mohammad M. Al
    Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, New Jersey 07102, United States.
    Mofid, Sohrab Alex
    NanoScience Technology Center, University of Central Florida, Orlando, Florida 32826, United States.
    Larsson, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oh, Kyu Hwan
    Department of Materials Science and Engineering, Seoul National University, Seoul 08826, South Korea.
    Ko, Dong-Kyun
    Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, New Jersey 07102, United States.
    Jung, Yeonwoong
    NanoScience Technology Center, University of Central Florida, Orlando, Florida 32826, United States; Department of Electrical and Computer Engineering and Department of Materials Science and Engineering, University of Central Florida, Orlando, Florida 32826, United States.
    Peel-and-Stick Integration of Atomically Thin Nonlayered PtS Semiconductors for Multidimensionally Stretchable Electronic Devices2022In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 14, no 17, p. 20268-20279Article in journal (Refereed)
    Abstract [en]

    Various near-atom-thickness two-dimensional (2D) van der Waals (vdW) crystals with unparalleled electromechanical properties have been explored for transformative devices. Currently, the availability of 2D vdW crystals is rather limited in nature as they are only obtained from certain mother crystals with intrinsically possessed layered crystallinity and anisotropic molecular bonding. Recent efforts to transform conventionally non-vdW three-dimensional (3D) crystals into ultrathin 2D-like structures have seen rapid developments to explore device building blocks of unique form factors. Herein, we explore a “peel-and-stick” approach, where a nonlayered 3D platinum sulfide (PtS) crystal, traditionally known as a cooperate mineral material, is transformed into a freestanding 2D-like membrane for electromechanical applications. The ultrathin (∼10 nm) 3D PtS films grown on large-area (>cm2) silicon dioxide/silicon (SiO2/Si) wafers are precisely “peeled” inside water retaining desired geometries via a capillary-force-driven surface wettability control. Subsequently, they are “sticked” on strain-engineered patterned substrates presenting prominent semiconducting properties, i.e., p-type transport with an optical band gap of ∼1.24 eV. A variety of mechanically deformable strain-invariant electronic devices have been demonstrated by this peel-and-stick method, including biaxially stretchable photodetectors and respiratory sensing face masks. This study offers new opportunities of 2D-like nonlayered semiconducting crystals for emerging mechanically reconfigurable and stretchable device technologies.

  • 46.
    Hedman, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Barzegar, Hamid Reza
    Department of Physics, Umeå University, Department of Physics, University of California.
    Rosén, Arne
    Physics Department, Göteborg University.
    Wågberg, Thomas
    Department of Physics, Umeå University.
    Larsson, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    On the Stability and Abundance of Single Walled Carbon Nanotubes2015In: Scientific Reports, E-ISSN 2045-2322, Vol. 5, article id 16850Article in journal (Refereed)
    Abstract [en]

    Many nanotechnological applications, using single-walled carbon nanotubes (SWNTs), are only possible with a uniform product. Thus, direct control over the product during chemical vapor deposition (CVD) growth of SWNT is desirable, and much effort has been made towards the ultimate goal of chirality-controlled growth of SWNTs. We have used density functional theory (DFT) to compute the stability of SWNT fragments of all chiralities in the series representing the targeted products for such applications, which we compare to the chiralities of the actual CVD products from all properly analyzed experiments. From this comparison we find that in 84% of the cases the experimental product represents chiralities among the most stable SWNT fragments (within 0.2 eV) from the computations. Our analysis shows that the diameter of the SWNT product is governed by the well-known relation to size of the catalytic nanoparticles, and the specific chirality is normally determined by the product’s relative stability, suggesting thermodynamic control at the early stage of product formation. Based on our findings, we discuss the effect of other experimental parameters on the chirality of the product. Furthermore, we highlight the possibility to produce any tube chirality in the context of recent published work on seeded-controlled growth.

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  • 47.
    Hedman, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Barzegar, Hamid Reza
    Department of Physics, Umeå University, Umeå, Sweden.
    Rosén, Arne
    Department of Physics, Göteborg University, Göteborg, Sweden.
    Wågberg, Thomas
    Department of Physics, Umeå University, Umeå, Sweden.
    Larsson, J. Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    The relation between stability and abundance of single walled carbon nanotubes2015Conference paper (Other academic)
    Abstract [en]

    The ability to utilize the remarkable electrical and mechanical properties of single walled carbon nanotubes (SWNTs) can be hugely beneficial for technological applications. The limiting factors for these technological applications is that many of them rely on specific electrical/mechanical properties of the SWNT. The mechanical and electrical properties of a SWNT depends on its chiral indecencies n and m, which means that in order to get a desired electrical/mechanical property one needs to synthesize SWNTs with specific chiral indecencies.Huge effort has been put on trying to synthesize SWNTs with specific chiral indecencies or to post-purify them after synthesis. Although post-purification methods can result in a relatively high yield of SWNTs with specific chiralities, such methods are expensive, time consuming and may damage the SWNTs. A more efficient method would be to selectively grow/synthesize SWNTs with the desired properties. Chemical vapor deposition (CVD) has become a favored technique for trying to achieve selective SWNT growth since the process involves several controllable growth parameters.In our work we have investigated the relation between the relative stability of different SWNTs and compared that to the experimentally observed statistical abundance of the same SWNTs. The relative energy of the SWNTs was calculated using density functional theory with the VASP-code. We have chosen to include all the SWNTs in the (n+m) = 8,9,10,11,12,13,14,15,16,17 and 18-series in our calculations, this equals 80 SWNTs in total. The SWNT models used in our calculations are six layered hydrogen terminated SWNT fragments where each layer contains 2(n+m) carbon atoms.Our calculations show a remarkable connection between the relative stability of the SWNTs and their statistical abundance in experiments. The most stable SWNT in each series correlates with the most abundant SWNT in that series, as found in the experimental results gathered from the literature.

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  • 48.
    Hedman, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Analytical modelling of single-walled carbon nanotube energies: the impact of curvature, length and temperature2020In: SN Applied Sciences, ISSN 2523-3963, E-ISSN 2523-3971, Vol. 2, no 3, article id 367Article in journal (Refereed)
    Abstract [en]

    Recent breakthroughs in the field of single-walled carbon nanotube (SWCNT) growth have been achieved by combining theoretical models with experiments. Theoretical models rely on accurate energies for SWCNTs, obtained via first principle calculations in the form of density functional theory (DFT). Such calculations are accurate, but time and resource intensive which limits the size and number of systems that can be studied. Here, we present a new analytical model consisting of three fundamental energy expressions, parametrized using DFT, for fast and accurate calculation of SWCNT energies at any temperature. Tests against previously published results show our model having excellent accuracy, with an root mean square error in total energies below 2 meV per atom as compared to DFT. We apply the model to study SWCNT growth on Ni catalysts at elevated temperatures by investigating the SWCNT/catalyst interface energy. Results show that the most stable interface shifts towards chiral edges as the temperature increases. The model’s ability to perform calculations at any temperature in combination with its speed and flexibility will allow researcher to study more and larger systems, aiding future research into SWCNT growth

  • 49.
    Hedman, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Length dependent stability of single-walled carbon nanotubes and how it affects their growth2017In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 116, p. 443-447Article in journal (Refereed)
    Abstract [en]

    Using density-functional theory the stability of armchair and zigzag single-walled carbon nanotubes and graphene nanoribbons was investigated. We found that the stability of armchair and zigzag nanotubes has different linear dependence with regard to their length, with switches in the most stable chirality occurring at specific lengths for each nanotube series. We explain these dependencies by competing edge and curvature effects. We have found that within each series armchair nanotubes are the most stable at short lengths, while zigzag nanotubes are the most stable at long lengths. These results shed new insights into why (near) armchair nanotubes are the dominant product from catalytic chemical vapor deposition growth, if templating is not used. Paradoxically, the stability of armchair nanotubes at short lengths favors their growth although zigzag nanotubes are more stable at long lengths, resulting in the production of the least stable nanotubes.

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  • 50.
    Hedman, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Research Center for Computational Design of Advanced Functional Materials, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
    Rothe, Tom
    Institute of Physics, Faculty of Natural Sciences, Chemnitz University of Technology, Chemnitz 09126, Germany.
    Johansson, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sandin, Fredrik
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Larsson, J. Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Miyamoto, Yoshiyuki
    Research Center for Computational Design of Advanced Functional Materials, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
    Impact of training and validation data on the performance of neural network potentials: A case study on carbon using the CA-9 dataset2021In: Carbon Trends, ISSN 2667-0569, Vol. 3, article id 100027Article in journal (Refereed)
    Abstract [en]

    The use of machine learning to accelerate computer simulations is on the rise. In atomistic simulations, the use of machine learning interatomic potentials (ML-IAPs) can significantly reduce computational costs while maintaining accuracy close to that of ab initio methods. To achieve this, ML-IAPs are trained on large datasets of images, which are atomistic configurations labeled with data from ab initio calculations. Focusing on carbon, we use deep learning to train neural network potentials (NNPs), a form of ML-IAP, based on the state-of-the-art end-to-end NNP architecture SchNet and investigate how the choice of training and validation data affects the performance of the NNPs. Training is performed on the CA-9 dataset, a 9-carbon allotrope dataset constructed using data obtained via ab initio molecular dynamics (AIMD). Our results show that image generation with AIMD causes a high degree of similarity between the generated images, which has a detrimental effect on the performance of the NNPs. But by carefully choosing which images from the dataset are included in the training and validation data, this effect can be mitigated. We conclude by benchmarking our trained NNPs in applications such as relaxation and phonon calculation, where we can reproduce ab initio results with high accuracy.

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