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  • 51.
    Muthukumar, Kaliappan
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Density Functional Theory Prediction of the Different Binding Sites For Ce in C78; C80 and C82 Cages Insights Through Electronic Structure2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Fullerenes; that have one metal atom encapsulated; are relatively well studied compared to species that have two elements inside the cage.1-5 Cerium; the most reactive elements of the rare earth group can be encapsulated into fullerene (C78; C80; C82) cages;1 which works as a n-dopant and in the incarcerated form it can be used as quantum bits in quantum computing2. Understanding of the position and the nature of binding of the metal atom inside the cage is important as it controls the structural and electronic properties of the molecule which in turn is essential in suggesting a novel candidate in the field of molecular electronics. Based on our DFT calculations; we have found that Ce prefers a specific and unique binding site in C82-C2v and has a C2v symmetric structure which we explain by the specific charge pattern of this binding site and the symmetry of the MO s that comply well with the Ce d orbital bonding.6 Analysis of all six membered rings of C80-Ih shows that all these rings have the distinct charge pattern; and therefore it is anticipated that two Ce atoms in Ce2@C80 should adapt to D2h symmetry where two Ce atoms binds with a center of a six-membered ring with a maximum distance due to the nature electrostatic repulsion between these two Ce atoms. But our DFT calculations show that Ce atoms in Ce2@C80 prefer a D3d configuration where two Ce atoms reside on-top of a carbon atom on the C3 axis of C80-Ih. We explain this fact by analyzing the electronic structure and expect similar things to happen in Ce2@C78. But in Ce2@C78 unlike Ce2@C80; Ce has its binding pattern as in Ce@C82 (binding to a center of a six-membered ring). We explain this variation in binding by analyzing its electronic structure and also explain the nature of the charge transfer between the Ce atoms and the cage (C82 and C80).

  • 52.
    Baran, Jakub D.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    DFT Computations of Metal Phthalocyanies on Ag(111)2008Konferensbidrag (Refereegranskat)
  • 53. Larsson, Andreas
    et al.
    Delaney, Paul
    Tyndall National Institute, University College Cork.
    Electronic structure of the nitrogen-vacancy center in diamond from first-principles theory2008Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, nr 16Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The nitrogen-vacancy (NV) center is a paramagnetic defect in diamond with applications as a qubit. Here, we investigate its electronic structure by using ab initio density functional theory for five different NV center models of two different cluster sizes. We describe the symmetry and energetics of the low-lying states and compare the optical frequencies obtained to experimental results. We compute the major transition of the negatively charged NV centers to within 25-100 meV accuracy and find that it is energetically favorable for substitutional nitrogens to donate an electron to NV0. The excited state of the major transition and the NV0 state with a neutral donor nitrogen are found to be close in energy

  • 54.
    Muthukumar, Kaliappan
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Explanation of the different preferential binding sites for Ce and la in M2@C80 (M = Ce, La2008Ingår i: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 18, nr 28, s. 3347-3351Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Metallofullerenes have many possible uses in technology and even in bio-medical applications. Some fullerenes have been found to have two incarcerated metal atoms such as M2@C80 (M = La, Ce, etc.). We have calculated the structural and electronic properties of Ce 2@C80 using density functional theory (DFT). Ce is known to be preferentially incorporated into the Ih symmetric C 80 isomer as La does in La2@C80. We have found that Ce2@C80 has a D3d symmetric ground state structure and that Ce binds to a different type of binding site compared to other cerium containing fullerenes, such as Ce@C82. This binding site also differs compared to La in La2@C80, which is D 2h symmetric. The two Ce atoms inside the C80-I h cage are equivalent and retain their f-electron. The Ce atoms bind on-top of one carbon atom (and its three neighbors) in Ce2@C 80, compared to in the center of a six-membered ring as in C 82. This novel binding site minimizes Ce(f)⋯Ce(f) overlap in favour of Ce-C bonding, giving the D3d configuration

  • 55. Larsson, Andreas
    et al.
    Delaney, Paul
    Queen's University Belfast.
    First-Principles Calculations of the Electronic Structure of the Nitrogen-Vacancy Center in Diamond2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Nitrogen-Vacancy or NV-center is a color center in diamonds containing atomic nitrogen [1]; in which the nitrogen and the vacancy are situated on neighboring lattice positions. The defect has C3v symmetry; with the nitrogen and the vacancy lying on the C3-axis. It has been well characterized experimentally: usually it is singly negatively charged; has a paramagnetic ground state (S=1) with spatial symmetry A2; and it has a strong dipole allowed 3A2 to 3E transition at 1.945 eV [2]. Recently the NV-center has been used as a qubit; and quantum NOT and controlled rotation (CROT) gates have been demonstrated [3] as well as optical read-out of the electronic spin state [4]. The NV-center has also been used as a single photon source [5;6]. Creating NV-centers in nanodiamonds could open up the possibility of placing NV-centers in an array as qubits in a quantum computer. In this work we present transition energies calculated from first-principles density functional theory (DFT) of the NV-center incorporated into two hydrogen-terminated nanodiamonds with approximate diameters of 1.2 nm and 1.5 nm [7]. We describe the symmetry and energetics of the low-lying states and compare the optical frequencies obtained to experimental results. We compute the major transition of the negatively charged NV-center to within 25 100 meV accuracy and find that it is energetically favourable for substitutional nitrogens to donate an electron to NV0. The excited state of the major transition and the NV0 state with a neutral donor nitrogen are found to be close in energy.

  • 56.
    Gannon, Greg
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Greer, James C.
    Tyndall National Institute, University College Cork.
    Thompson, Damien J.
    Tyndall National Institute, University College Cork.
    Guanidinium chloride molecular diffusion in aqueous and mixed water-ethanol solutions2008Ingår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 112, nr 30, s. 8906-8911Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Solutions containing guanidinium chloride (GdmCl), or equivalently guanidine hydrochloride (GdnHCl), are commonly used to denature macromolecules such as proteins and DNA in, for example, microfluidics studies of protein unfolding. To design and study such applications, it is necessary to know the diffusion coefficients for GdmCl in the solution. To this end, we use molecular dynamics simulations to calculate the diffusion coefficients of GdmCl in water and in water-ethanol solutions, for which no direct experimental measurements exist. The fully atomistic simulations show that the guandinium cation Gdm + diffusion decreases as the concentration of both Gdm + and ethanol in the solution increases. The simulations are validated against available literature data, both transformed measured viscosity values and computed diffusion coefficients, and we show that a prudent choice of water model, namely TIP4P-Ew, gives calculated diffusion coefficients in good agreement with the transformed measured viscosity values. The calculated Gdm + diffusion behavior is explained as a dynamic mixture of free cation, stacked cation, and ion-paired species in solution, with weighted contributions to Gdm + diffusion from the stacked and paired states helping explain measured viscosity data in terms of atom-scale dynamics

  • 57.
    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 Study2008Konferensbidrag (Refereegranskat)
    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).

  • 58.
    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 Study2008Konferensbidrag (Refereegranskat)
  • 59.
    Muthukumar, Kaliappan
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Metallofullerenes in Technology: Doping and Surface Binding2008Konferensbidrag (Refereegranskat)
  • 60.
    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 applications2008Konferensbidrag (Refereegranskat)
    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

  • 61. Larsson, Andreas
    Modelling Nanostructured Carbon Materials for Future ICT Applications2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Carbon nanotubes (CNTs) have, due to their remarkable mechanical, electronic and thermal properties, many suggested uses, and have even been demonstrated as interconnects and nano-transistors in laboratory built devices [1-4]. This is an important effort since metallic CNTs have lower resistivity than Cu, and semiconducting CNTs have higher mobility than Si, which are traits that could help push the boundaries of Moore s law even further. The reason CNTs are not yet incorporated into electronics is due to growth control and placement issues. With present day state-of-the-art techniques it is not possible to grow CNTs with only one property (i.e. either all metallic or all semiconducting), which presents the first and principal hurdle for the utilisation of CNTs in semiconductor industry. It is, however, possible to grow CNTs of a certain type (multi-walled, double-walled, or single walled), within a rather narrow diameter distribution. It is also well understood how the orientation of the honey-comb structure relative to the CNT axis determines the property of the CNT itself. The problem lies in realizing growth of CNTs with control over this internal graphene structuring. We have performed first-principles calculations of how single-walled carbon nanotubes (SWNTs) bond with different metal nanoparticles explaining why the traditional catalysts (Fe, Co, Ni) are more successful than other metals (Cu, Pd, Au) [5], and how this realization relates to new nanocomposite catalyst particles (Cu/Mo) [6]. We will present our contribution to understanding the mechanism of CNT growth, since it is only through better knowledge that property-controlled growth of CNTs can be achieved

  • 62. Larsson, Andreas
    et al.
    Kolodziejczyk, J.
    Baran, J.D.
    Larsson, Peter O.
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Ahuja, Rajeev B.
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Bolton, Kim
    Physics Department, Göteborg University.
    Ding, Feng
    Physics Department, Göteborg University.
    Rosen, Arne E.
    Physics Department, Göteborg University.
    Modelling of Carbon Nanotube Catalytic Growth2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Carbon nanotubes (CNTs) have; due to their remarkable mechanical; electronic and thermal properties; many suggested uses; and have even been demonstrated as interconnects and nano-transistors in laboratory built devices [1-4]. The reason CNTs are not yet incorporated into electronics is due to growth control and placement issues. With present day state-of-the-art techniques it is not possible to grow CNTs with only one property (i.e. either all metallic or all semiconducting); which presents the first and principal hurdle for the utilisation of CNTs in semiconductor industry. It is; however; possible to grow CNTs of a certain type (multi-walled; double-walled; or single walled); within a rather narrow diameter distribution. It is also well understood how the orientation of the honey-comb structure relative to the CNT axis determines the property of the CNT itself. The problem lies in realizing growth of CNTs with control over this internal graphene structuring. We have performed first-principles calculations of how single-walled carbon nanotubes (SWNTs) bond with different metal nanoparticles explaining why the traditional catalysts (Fe; Co; Ni) are more successful than other metals (Cu; Pd; Au) [5]; and how this realization relates to new nanocomposite catalyst particles (Cu/Mo) [6]. We will present our contribution to understanding the mechanism of catalytic CNT growth; since it is only through better knowledge that property-controlled growth of CNTs can be achieved

  • 63. Larsson, Andreas
    et al.
    Fagas, G.
    Greer, James C.
    National Institute, Lee Makings, Prospect Row, Cork.
    Martinez, C.
    Patterson, J.
    Nikonov, D.
    Park, S.
    Haverty, M.G.
    Shankar, S.
    Multi-Scale Simulation for Nanowires and Carbon Nanotubes2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    With the advent of nanotechnology; semiconductor processing is driving developments in computational chemis-try and computational material science. Describing materials from an atomic perspective allows for simulations that describe the formation of and flow of electrons in nanoscale structures. However; to achieve design for mi-croelectronics technologies requires atomic scale simulations that span varying length and time scales. In this presentation; developments toward a strategy for simulating nanowire and carbon nanotubes; their electronic structure; and electron and phonon transport within a single simulation hierarchy is described.

  • 64. Larsson, Andreas
    et al.
    Elliott, Simon D.
    Tyndall National Institute, University College Cork.
    Greer, James C.
    Tyndall National Institute, University College Cork.
    Repp, Jascha
    IBM Research, Zurich Research Laboratory.
    Meyer, Gerd
    IBM Research, Zurich Research Laboratory.
    Allenspach, Rolf
    IBM Research, Zurich Research Laboratory.
    Orientation of individual C60 molecules adsorbed on Cu(111): Low-temperature scanning tunneling microscopy and density functional calculations2008Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, nr 11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Density functional theory (DFT) and low-temperature scanning tunneling microscopy (STM) have been combined to examine the bonding of individual C60 molecules on Cu(111). Energy-resolved differential-conductance maps have been measured for individual C60 molecules adsorbed on a Cu(111) surface by means of low-temperature STM, which are compared to and complemented by theoretically computed spectral images. It has been found that C60 chemisorbs with a six-membered ring parallel to the surface at two different Cu(111) binding sites that constitute two exclusive hexagonal sublattices. On each sublattice, C60 is bonded in one particular rotational conformer, i.e., C60 molecules bind to the Cu(111) surface in two different azimuthal orientations differing by 60°depending on which sublattice the binding site belongs to. The binding conformation of C60 and its orientation with regard to the copper surface can be deduced by this joint experimental-theoretical approach. Six possible pairs of C60 configurations on three different Cu surface binding sites have been identified that fulfil the requirements of the two sublattices and are consistent with all experimental and theoretical data. Theory proposes that two of these configuration pairs are most likely. We have found that DFT does not get the binding energy between rotational conformers in the correct order. We also report two different C60 monolayers on Cu(111): one with alternating orientations of neighboring molecules at low temperature and the other with (4×4) structure after annealing above room temperature.

  • 65.
    Stróecka, Anna
    et al.
    Peter Grünberg Institut (PGI-3), JARA, Forschungszentrum Jülich.
    Muthukumar, Kaliappan
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Mysliveček, Josef
    Charles University, Faculty of Mathematics and Physic.
    Voigtländer, Bert
    Peter Grünberg Institut (PGI-3), JARA, Forschungszentrum Jülich.
    Phonon-assisted transport through a single endohedrally doped fullerene2008Konferensbidrag (Refereegranskat)
  • 66.
    Larsson, Peter O.
    et al.
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Araújo, Carlos Moysés
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Larsson, Andreas
    Jena, Puru
    Department of Physics, Virginia Commonwealth University, Richmond.
    Ahuja, Rajeev B.
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Role of catalysts in dehydrogenation of MgH2 nanoclusters2008Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 105, nr 24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A fundamental understanding of the role of catalysts in dehydrogenation of MgH2 nanoclusters is provided by carrying out first-principles calculations based on density functional theory. It is shown that the transition metal atoms Ti, V, Fe, and Ni not only lower desorption energies significantly but also continue to attract at least four hydrogen atoms even when the total hydrogen content of the cluster decreases. In particular, Fe is found to migrate from the surface sites to the interior sites during the dehydrogenation process, releasing more hydrogen as it diffuses. This diffusion mechanism may account for the fact that a small amount of catalysts is sufficient to improve the kinetics of MgH2, which is essential for the use of this material for hydrogen storage in fuel-cell applications

  • 67.
    Kołodziejczyk, Wojciech
    et al.
    Tyndall National Institute, University College Cork.
    Baran, Jakub D.
    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
    Stability of Single-Walled Carbon Nanotubes and Their Cut Ends2008Konferensbidrag (Refereegranskat)
  • 68.
    Muthukumar, Kaliappan
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Structural and Electronic Properties of Cerium Containing (Ce@C60; Ce@C80; Ce@C82 and Ce2@C80) Metallofullerenes2008Konferensbidrag (Refereegranskat)
  • 69.
    Muthukumar, Kaliappan
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Schulte, Karina H.G
    Moriarty, Philip J.
    Stróecka, Anna
    Institut für Bio- und Nanosysteme, Forschungszentrum Jülich.
    Voigtländer, Bert
    Institut für Bio- und Nanosysteme, Forschungszentrum Jülich.
    Surprising Findings for Ce Doped Fullerenes and Understanding of Experiments through Theoretical Modelling A DFT Approach2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Endohedral fullerenes; which have one metal atom encapsulated; are relatively well studied compared to species that have two elements inside the cage.1-5 Cerium; the most reactive elements of the rare earth group can be encapsulated into fullerene (C78; C80; C82) cages;1 which works as a n-dopant and in the incarcerated form it can be used as quantum bits in quantum computing2. Understanding of the position and binding pattern of the metal atom inside the cage is important as it controls the structural and electronic properties of the molecule. We found that Ce in Ce@C82 has a specific and unique binding site in C82-C2v and has a C2v symmetric structure; which is explained by the specific charge pattern of this binding site and the symmetry of the MO s that comply well with the Ce d orbital bonding.6 This six-membered ring binding site is also favored by La in La@C82. Each of the six-membered rings of C80-Ih fulfills this symmetry criterion and therefore a similar kind of binding site is expected for Ce in Ce2@C80. But; we observe a novel binding site for Ce in presence of an additional cerium atom; while La preserve its usual binding pattern in La2@C80 as in La@C82.7 We here discuss and analyze the reason for the preference of novel binding site of Ce atoms in C80-Ih by explaining the competitive binding nature of Ce-Ce and Ce-C. Surprisingly; Ce in Ce2@C78 unlike Ce2@C80 has its binding pattern as in Ce@C60 and in Ce@C82 (binding to a six-membered ring). We explain this variation in binding together with the nature of the charge transfer between the Ce atoms and the cage (C82 and C80). In addition; we explain experimental observations for Ce@C82 and Ce2@C80 from RESPES; IETS; STM/STS spectra by comparison with simulated properties

  • 70.
    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 nanotubes2008Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, nr 2, s. 463-468Artikel i tidskrift (Refereegranskat)
    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

  • 71.
    Muthukumar, Kaliappan
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Stróżecka, Anna
    Institut für Bio- and Nanosysteme (IBN 3) and CNI – Forschungszentrum Jülich.
    Voigtländer, Bert
    Institut für Bio- and Nanosysteme (IBN 3) and CNI – Forschungszentrum Jülich.
    Schulte, Kristina H.G.
    AX-lab, Lund University.
    Moriarty, Philip J.
    School of Physics and Astronomy, University of Nottingham.
    Theoretical Predictions and Explanation of Experimental Observations for Ce Doped Fullerenes2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Fullerenes that have one metal atom encapsulated; for example M@C60; M@C70; M@C82; (M= Sc; Y; La; Ce; etc.) are relatively well studied compared to species that have two elements inside the cage.1-4 We recently reported the structure of Ce@C82 and explained the preferential binding site of Ce to only one of the thirty-one 6-membered rings of C82-C2v cage by identifying its specific charge pattern and the symmetry of the MO s that comply well with the Ce d orbital bonding.5 Since; each of the six-membered rings of C80-Ih fulfill the proposed criteria; similar kind of binding site is expected for Ce in Ce2@C80. But; we observe a novel binding site for Ce in presence of an additional cerium atom; while La in La2@C80 does bond with six-membered rings.6 In this study; we discuss and analyze the reason for the preference for a novel binding site by Ce atoms in C80-Ih through density functional calculations. Further; we explain the nature of the charge transfer between the Ce atoms and the cage (C82 and C80) and elucidate the oxidation state of Ce in these metallofullerenes by comparing the charge transfer in the conventional Ce tri halides (CeF3; CeBr3). In addition; we explain experimental observations for Ce@C82 and Ce2@C80 from RESPES; IETS; STM/STS spectra by comparison with simulated properties

  • 72.
    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 Inversion2008Konferensbidrag (Refereegranskat)
    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

  • 73.
    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 monolayers2007Konferensbidrag (Refereegranskat)
  • 74.
    Larsson, Peter O.
    et al.
    Department of Physics, University of Uppsala.
    Araújo, Carlos Moysés
    Department of Physics, University of Uppsala.
    Larsson, Andreas
    Jena, Puru
    Department of Physics, Virginia Commonwealth University, Richmond.
    Ahuja, Rajeev B.
    Department of Physics, University of Uppsala.
    Activities and whereabouts of transition metal atom catalysts in MgH2 nanoclusters2007Konferensbidrag (Refereegranskat)
  • 75.
    Larsson, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Activity: Reversible Conformational Inversion of SnPc and PbPc molecules2007Konferensbidrag (Övrig (populärvetenskap, debatt, mm))
  • 76.
    Larsson, Peter O.
    et al.
    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.
    Yakobson, Boris I.
    ME and MS Department, Rice University, Houston.
    Duan, HaiMing
    Physics Department, Göteborg University.
    Rosén, Arne E.
    Physics Department, Göteborg University.
    Bolton, Kim
    Physics Department, Göteborg University.
    Calculating carbon nanotube-catalyst adhesion strengths2007Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, nr 11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Density-functional theory is used to assess the validity of modeling metal clusters as single atoms or rings of atoms when determining adhesion strengths between clusters and single-walled carbon nanotubes (SWNTs). Representing a cluster by a single atom or ring gives the correct trends in SWNT-cluster adhesion strengths (Fe≈Co>Ni), but the single-atom model yields incorrect minimum-energy structures for all three metals. We have found that this is because of directional bonding between the SWNT end and the metal cluster, which is captured in the ring model but not by the single atom. Hence, pairwise potential models that do not describe directional bonding correctly, and which are commonly used to study these systems, are expected to give incorrect minimum-energy structures

  • 77.
    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 Mechanisms2007Ingår i: 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], 2007Konferensbidrag (Refereegranskat)
    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.

  • 78.
    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 Growth2007Konferensbidrag (Refereegranskat)
  • 79.
    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).2007Konferensbidrag (Refereegranskat)
    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

  • 80.
    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)2007Konferensbidrag (Refereegranskat)
    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.

  • 81.
    Muthukumar, Kaliappan
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    DFT Study of Ce2@C80 Comparison with La2@C802007Konferensbidrag (Refereegranskat)
    Abstract [en]

    Many rare earth elements have been encapsulated in fullerene cages and their possible applications include quantum bits in quantum computing; MRI agents in bio-medical sciences and as superconductors; which have made them interesting species both as a molecule and as a material.1 Among such available fullerenes; Ih-C80 has interesting chemistry as the unstable isomer gets stabilized by encapsulating two metal atoms such as M2@C80 (M=La; Ce etc.).3 Ce2@C80 is one such species and is reported to be extracted over a decade ago; but until now only a few studies exploring its nature have been reported.4;5 Top and Side view of Ce2@C80 Hence; we have applied density functional theory to expand the investigation of Ce2@C80 further to have a closer look at its structural and electronic properties. Our calculations reveal preferential binding sites of the two Ce inside the Ih-C80 cage; which differs from other cerium containing fullerenes such as Ce@C82.6 The reason for this will be discussed and compared with experiments and with the results available for La2@C80.

  • 82.
    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)2007Konferensbidrag (Refereegranskat)
  • 83.
    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 applications2007Konferensbidrag (Refereegranskat)
    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

  • 84.
    Stróżecka, Anna
    et al.
    Peter Grünberg Institut (PGI-3), and JARA-Fundamentals of Future Information Technology, Forschungszentrum Jülich.
    Muthukumar, Kaliappan
    Tyndall National Institute, University College Cork.
    Dybek, Aneta
    Department of Physics, Queen Mary University of London.
    Mysliveček, Josef
    Charles University, Faculty of Mathematics and Physic.
    Larsson, Andreas
    Dennis, John S.
    Department of Physics, Queen Mary University of London.
    Voigtländer, Bert
    Peter Grünberg Institut (PGI-3), and JARA-Fundamentals of Future Information Technology, Forschungszentrum Jülich.
    Scanning Tunneling Spectroscopy of Cerium Metallofullerenes2007Konferensbidrag (Refereegranskat)
  • 85.
    Stróżecka, Anna
    et al.
    Peter Grünberg Institut (PGI-3), and JARA-Fundamentals of Future Information Technology, Forschungszentrum Jülich.
    Muthukumar, Kaliappan
    Tyndall National Institute, University College Cork.
    Dybek, Aneta
    Department of Physics, Queen Mary University of London.
    Mysliveček, Josef
    Charles University, Faculty of Mathematics and Physic.
    Larsson, Andreas
    Dennis, John S.
    Department of Physics, Queen Mary University of London.
    Voigtländer, Bert
    Peter Grünberg Institut (PGI-3), and JARA-Fundamentals of Future Information Technology, Forschungszentrum Jülich.
    Scanning Tunnelling Spectroscopy of Ce@C82 and Ce2@C80 Metallofullerenes2007Konferensbidrag (Refereegranskat)
  • 86.
    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 growth2007Konferensbidrag (Refereegranskat)
  • 87.
    Muthukumar, Kaliappan
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Structural and Electronic Characterization of Ce2@C80: Insights through DFT Computations2007Konferensbidrag (Refereegranskat)
  • 88.
    Muthukumar, Kaliappan
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Schulte, Kristina H.G.
    AX-lab, Lund University.
    Moriarty, Philip J.
    School of Physics and Astronomy, University of Nottingham.
    Stróżecka, Anna
    Institut für Bio- and Nanosysteme (IBN 3) and CNI – Forschungszentrum Jülich.
    Voigtländer, Bert
    Institut für Bio- and Nanosysteme (IBN 3) and CNI – Forschungszentrum Jülich.
    Structural, Vibrational, and Electronic Characterization of Ce@C82: A Joint DFT and Experimental Study2007Konferensbidrag (Refereegranskat)
  • 89.
    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 molecules2006Ingår i: IEEE transactions on nanotechnology, ISSN 1536-125X, E-ISSN 1941-0085, Vol. 5, nr 6, s. 745-749Artikel i tidskrift (Refereegranskat)
    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

  • 90.
    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 systems2006Konferensbidrag (Refereegranskat)
  • 91.
    Larsson, Peter
    et al.
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Ding, Feng
    Physics Department, Göteborg University.
    Larsson, Andreas
    Ahuja, Rejeev B.
    Condensed Matter Theory Group, Department of Physics, Uppsala Universitet.
    Rosén, Arne E.
    Physics Department, Göteborg University.
    Bolton, Kim
    Physics Department, Göteborg University.
    Bond strength between single-walled carbon nanotubes (SWNTs) and metal clusters: implication for catalytic growth2006Konferensbidrag (Refereegranskat)
  • 92. Larsson, Peter
    et al.
    Ding, Feng
    Physics Department, Göteborg University.
    Larsson, Andreas
    Rosén, Arne E.
    Physics Department, Göteborg University.
    Aruja, Rejeev B.
    Department of Physics, Condensed Matter Theory Group, Uppsala University.
    Bolton, Kim
    Physics Department, Göteborg University.
    Carbon nanotube-metal cluster bond strenghts: implications for catalytic growth2006Konferensbidrag (Refereegranskat)
  • 93.
    Muthukumar, Kaliappan
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    DFT Study of Ce2@C82: comparison betwwn cerium and lanthanum inside C822006Konferensbidrag (Refereegranskat)
  • 94.
    Muthukumar, Kaliappan
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Electronic Structure and Vibrational Spectrum of Ce@C82 – Insights through DFT Computations2006Konferensbidrag (Refereegranskat)
  • 95.
    Thompson, Damien J.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    Modeling competitive guest binding to β-cyclodextrin molecular printboards2006Ingår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, nr 33, s. 16640-16645Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Anchoring of functionalized guest molecules to self-assembled monolayers (SAMs) is key to the development of molecular printboards for nanopatterning. One very promising system involves guest binding to immobilized β-cyclodextrin (β-CD) hosts, with guest:host recognition facilitated by a hydrophobic interaction between uncharged anchor groups on the guest molecule and β-CD hosts self-assembled at gold surfaces. We use molecular dynamics free energy (MDFE) simulations to describe the specificity of guest:β-CD association. We find good agreement with experimental thermodynamic measurements for binding enthalpy differences between three commonly used phenyl guests: benzene, toluene, and t-butylbenzene. van der Waals interaction with the inside of the host cavity accounts for almost all of the net stabilization of the larger phenyl guests in β-CD. Partial and full methylation of the secondary rim of β-CD decreases host rigidity and significantly impairs binding of both phenyl and larger adamantane guest molecules. The β-CD cavity is also very intolerant of guest charging, penalizing the oxidized state of ferrocene by at least 7 kcal/mol. β-CD hence expresses moderate specificity toward uncharged organic guest molecules by van der Waals recognition, with a much higher specificity calculated for electrostatic recognition of organometallic guests.

  • 96.
    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 Growth2006Konferensbidrag (Refereegranskat)
  • 97.
    Larsson, Peter
    et al.
    Department of Physics, University of Uppsala.
    Araújo, Carlos Moysés
    Department of Physics, University of Uppsala.
    Larsson, Andreas
    Jena, Puru
    Department of Physics, Virginia Commonwealth University, Richmond.
    Ahuja, Rajeev B.
    Department of Physics, University of Uppsala.
    Theoretical investigation of catalysed MgH22006Konferensbidrag (Refereegranskat)
    Abstract [en]

    MgH2 has attracted much attention for being a good hydrogen storage material due to its light weight, low manufacturing cost and high storage capacity (7.6 wt%). But its slow absorption/desorption kinetics and high dissociation temperature (nearly 300 C) limit its practical applications for hydrogen storage. To overcome this, much effort has been paid mainly by making nanocrystalline Mg and/or by adding alloying elements. In this work, we provide a theoretical investigation of the electronic and structural properties of pure and M-doped MgH2 (with M=Sc, Ti, V, Fe, Ni, Al). We have made calculations for both the crystalline state and 1.0 nm particles. The self-consistent total energy calculations are performed within density functional theory using the VASP package for crystals and TURBOMOLE package for clusters. One aim of this study is to see if the alloying elements can weaken the Mg-H bonds, resulting in improved thermodynamics and faster kinetics. Another one is to understand the differences in the thermodynamics of clusters and crystals

  • 98. Larsson, Andreas
    et al.
    Delaney, Paul
    Queen's University Belfast.
    Theoretical investigation of the hardness of nanodiamonds and the energetics of the NV-centre2006Konferensbidrag (Refereegranskat)
  • 99.
    Thompson, Damien J.
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    A molecular dynamics free energy study of competitive guest binding to β-cyclodextrin2005Konferensbidrag (Refereegranskat)
  • 100.
    Larsson, Peter O.
    et al.
    Department of Physics, University of Uppsala.
    Araúj, Carlos Moysés
    Department of Physics, University of Uppsala.
    Larsson, Andreas
    Ahuja, Rajeev B.
    Department of Physics, University of Uppsala.
    An ab initio study of the crystalline and nanostructured pure and m-dpoed MgH22005Konferensbidrag (Refereegranskat)
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