David Tománek - Academia.edu (original) (raw)
Papers by David Tománek
Journal of Physics and …, 1992
Superconductivity observed in alkali-intercalated, solid C 60 can be explained on the basis of co... more Superconductivity observed in alkali-intercalated, solid C 60 can be explained on the basis of conventional Bardeen-Cooper-Schrieffer theory. Intramolecular Jahn-Teller-type vibrations with high frequencies couple to conduction electrons in C 60 7T" orbitals with strength V. The density of these states (N) is determined by the relatively weak intermolecular coupling. This results in a real space factorization of the coupling parameter A=NV, which has several experimental consequences. We present detailed calculations that lead to this picture and compare these with existing experiments.
Bulletin of the American Physical Society, 2016
Bulletin of the American Physical Society, 2014
Submitted for the MAR14 Meeting of The American Physical Society Local curvature and relative sta... more Submitted for the MAR14 Meeting of The American Physical Society Local curvature and relative stability of graphitic carbon nanostructures 1 JIE GUAN, ZHONGQI JIN, DAVID TOMANEK, Michigan State University-We propose a way to estimate the relative stability of graphitic nanostructures including fullerenes, nanotubes and schwarzites using continuum elasticity theory. The key quantity is the local deformation energy with respect to graphene, which we determine by estimating the two principal radii of curvature at each lattice site using the Bertrand-Diquet-Puiseux theorem. We find an impressive level of agreement between strain energies based on local curvature and ab initio density functional calculations. We demonstrate that our approach correctly determines strain energy differences between nanotubes with different chiral indices (n,m) and zero Gaussian curvature, C n fullerenes with 20≤n≤72 atoms and positive Gaussian curvature, and selected schwarzites with negative Gaussian curvature. In contrast to other methods, our approach correctly determines even the energy differences between different isomers of fullerenes such as C 28 , C 36 and C 38 .
Bulletin of the American Physical Society, 2005
ABSTRACT
Bulletin of the American Physical Society, 2007
We investigate the effect of atomic ordering and geometry on the relative stability and electroni... more We investigate the effect of atomic ordering and geometry on the relative stability and electronic as well as magnetic structure of Mo6S9-xIx nanowires using ab initio Spin Density Functional calculations. The skeleton of these unusually stable nanowires consists of Mo octahedra, which are decorated with S and I atoms and connected by sulfur bridges. These sulfur bridges turn out to be bi-stable, providing the nanowires with the unusual capability to stretch by 20% at no energy cost. Depending on the degree the nanowires have been stretched, they may reversibly acquire or lose their magnetic moment. The ordering of the decorating atoms, observed in these nanowires, reflects our finding that the total energy depends sensitively on the atomic arrangement at a given stoichiometry.
Physics Letters A, 1986
Abstract A simple criterion is introduced which allows one to estimate the tendency of metal surf... more Abstract A simple criterion is introduced which allows one to estimate the tendency of metal surfaces to reconstruct. At clean surfaces changes in surface tension γ 0 are estimated from a simple formula based on a tight-binding hamiltonian, yielding surface multilayer relaxations as by-product. The effect of adsorbates to induce or to suppress reconstruction is described by adsorbate-dependent modifications of γ 0 . The calculation successfully describes reconstruction at clean and adsorbate-covered (110) and (100) surfaces of Ir, Pt and Au.
Physical Review Letters, 2011
Physical Review Letters, 2012
We use ab initio density functional calculations to study the formation and structural as well as... more We use ab initio density functional calculations to study the formation and structural as well as thermal stability of cellular foam-like carbon nanostructures. These systems with a mixed sp 2 /sp 3 bonding character may be viewed as bundles of carbon nanotubes fused to a rigid contiguous 3D honeycomb structure that can be compressed more easily by reducing the symmetry of the honeycombs. The foam may accommodate the same type of defects as graphene, and its surface may be be stabilized by terminating caps. We postulate that the foam may form under non-equilibrium conditions near grain boundaries of a carbon-saturated metal surface.
Physical Review Letters, 2004
We propose a new microscopic mechanism to explain the unusually fast fusion process of carbon nan... more We propose a new microscopic mechanism to explain the unusually fast fusion process of carbon nanotubes. We identify the detailed pathway for two adjacent (5,5) nanotubes to gradually merge into a (10,10) tube, and characterize the transition states. The propagation of the fused region is energetically favorable and proceeds in a morphology reminiscent of a Y junction via a zipper mechanism, involving only Stone-Wales bond rearrangements with low activation barriers. The zipper mechanism of fusion is supported by a time series of high-resolution transmission electron microscopy observations.
Angewandte Chemie, 2013
ABSTRACT Diamant‐Nanodrähte bilden sich innerhalb von Kohlenstoff‐Nanoröhren durch Tempern von Di... more ABSTRACT Diamant‐Nanodrähte bilden sich innerhalb von Kohlenstoff‐Nanoröhren durch Tempern von Diamantan‐4,9‐dicarbonsäure in einer Wasserstoffatmosphäre. H. Shinohara et al. beschreiben in der Zuschrift auf S. 3805 ff. die Synthese und den Nachweis dieser Nanodrähte. Das Bild zeigt das Eintragen von Diamantan‐4,9‐dicarbonsäure in doppelwandige Kohlenstoff‐Nanoröhren mit offenen Enden, das Tempern unter Wasserstoff (roter “Rauch”) und die Umwandlung in Diamant‐Nanodrähte (goldene Strukturen).
Alkali metal adducts to LOGEAs (Large Organic Globular Electron Acceptors) share with superconduc... more Alkali metal adducts to LOGEAs (Large Organic Globular Electron Acceptors) share with superconducting `Buckyball` adducts such as K3C60 the globular shape, delocalized pi systems and accessible reduction potentials that are believed important for superconductivity. This research focused on the synthesis and study of reduced macrobicyclic Schiff-base cryptands that have an aromatic linking group in each of the three strands. Some samples, when reduced with Rb or K, showed LFMA (Low Frequency Microwave Absorption) up to 50 K and/or a pronounced diamagnetic downturn in the susceptibility below 30 K. These phenomena are usually associated with superconductivity. The magnitude of these effects was, however, only that expected for traces (<1%) of superconducting phases and the effects were only present in a few samples. Much effort over a two-year time span was directed toward the identification and isolation of the phase(s) responsible, but without success. Although superconductivity could not be verified, these studies opened a new area of research; the study of the solid state behavior of radical anion salts. Except for some crystal structure determinations, this field is virtually unexplored and is likely to lead to potentially useful electronic and magnetic materials. The stability at and above room temperature, even of multiply reduced compounds, is especially encouraging.
FIG.1. Calculated electron density difference ∆ρ=ρtot(bulk)−Σρtot(monolayers) representing the ch... more FIG.1. Calculated electron density difference ∆ρ=ρtot(bulk)−Σρtot(monolayers) representing the charge redistribution caused by assembling the bulk structure from isolated monolayers. (a) Diffusion Monte Carlo (DMC) isosurfaces bounding regions of excess electron density (dark brown) and electron deficiency (light brown), with respective values ±6.5×10 e/Å. (b) <∆ρ(z)> for DMC and selected DFT functionals averaged across the x−y plane of the layers, with z/c indicating the relative position of the plane in the unit cell. (From Ref. [3]). If graphene had a band gap, it would probably be the optimum 2D system for electronics applications. Layered transition metal dichalcogenides (TMDs) with a robust intrinsic band gap appear as the next-best alternative. Only after a long search, however, optimum strategies have been devised to make low-resistance, ohmic contacts to TMDs [1]. In the meantime, a new class of 2D semiconductors has been rapidly gaining attention, namely layered blac...
The mechanical response of carbon nanotubes to revere deformation has attracted much attention si... more The mechanical response of carbon nanotubes to revere deformation has attracted much attention since their discovery in 1991. Carbon nanotubes have already demonstrated exceptional mechanical properties: their excellent flexibility during bending have been observed experimentally. Nanotubes combine high stiffness with elasticity and the ability to buckle and collapse in a reversible manner even largely axially compressed or twisted deformation. For these reasons, it has been suggested that carbon nanotubes could be promising candidates for a new generation of extremely light and super strong fiver. However, experiments probing the strength of nanotubes are very challenging, but to the difficulties in growing high quality, defect-free nanotubes of sufficient length and in measuring the strength of nanoscale objects. Theoretically, investigating the strength of carbon nanotubes requires modeling of inherently mesoscopic phenomena, such as plasticity and fracture on a microscopic compo...
The unique electronic transport behavior of quasi-1D carbon nanotubes(Stefano Sanvito, Young-Kyun... more The unique electronic transport behavior of quasi-1D carbon nanotubes(Stefano Sanvito, Young-Kyun Kwon, David Tomanek, and Colin J. Lambert, Phys. Rev. Lett. 84), 1974 (2000). finds an unexpected counterpart in their unusually high thermal conductance.(Savas Berber, Young-Kyun Kwon, and David Tomanek, Phys. Rev. Lett. 84), 4613 (2000). The latter is a consequence of the structural rigidity of nanotubes, resulting in a large sound velocity, and their phonon structure. Soft phonon modes, primarily associated with tube bending and twisting, are essentially decoupled from the energy-carrying hard phonon modes which originate in the stretching and bending of interatomic bonds. The absence of an efficient coupling mechanism between these different phonon modes is responsible for their low damping and a long phonon mean free path. With a peak value lambda=37,000W/m/K at 100K, the thermal conductance of an isolated (10,10) nanotube, predicted using non-equilibrium molecular dynamics simulations, is comparable to that of isotopically pure diamond. At room temperature, the predicted value lambda=6,600W/m/K even exceeds that of this best thermal conductor. Unlike bulk graphite, where coupling between the flexible layers reduces the basal plane thermal conductance by one order of magnitude, we find that the inter-tube coupling in nanotube ropes does not reduce the single-tube conductance significantly.
Bulletin of the American Physical Society, 2014
A study of the electronic structure of carbon nanoparticles has been carried out using the method... more A study of the electronic structure of carbon nanoparticles has been carried out using the methods of quantum chemistry and X-ray emission spectroscopy. Fragments of (n, 0) tubes with n = 6, ... ,11 and of (5,5)-(10,0) tubes were calculated using PM3 method. The dependence of the electronic structure of the fragment on length and symmetry was investigated. The structure of the frontier orbitals was shown to change regularly depending on the tube chirality. Band structure of (n,O) and (5,5) tubes was studied by the tight-binding method. A comparison of the basic blocks of the molecular orbitals (MOs) of the fragment and bands of (6,0) and (5,5) tubes was carried out. Experimental CKo spectra. for single-wall and multiwall carbon nanotubules were obtained. These spectra agree satisfactorily with the theoretical spectra plotted as the results of cluster calculations. The structure of the valence zone for the central hexagons of the nanotube fragments keeps the basic features in the ser...
Journal of Physics and …, 1992
Superconductivity observed in alkali-intercalated, solid C 60 can be explained on the basis of co... more Superconductivity observed in alkali-intercalated, solid C 60 can be explained on the basis of conventional Bardeen-Cooper-Schrieffer theory. Intramolecular Jahn-Teller-type vibrations with high frequencies couple to conduction electrons in C 60 7T" orbitals with strength V. The density of these states (N) is determined by the relatively weak intermolecular coupling. This results in a real space factorization of the coupling parameter A=NV, which has several experimental consequences. We present detailed calculations that lead to this picture and compare these with existing experiments.
Bulletin of the American Physical Society, 2016
Bulletin of the American Physical Society, 2014
Submitted for the MAR14 Meeting of The American Physical Society Local curvature and relative sta... more Submitted for the MAR14 Meeting of The American Physical Society Local curvature and relative stability of graphitic carbon nanostructures 1 JIE GUAN, ZHONGQI JIN, DAVID TOMANEK, Michigan State University-We propose a way to estimate the relative stability of graphitic nanostructures including fullerenes, nanotubes and schwarzites using continuum elasticity theory. The key quantity is the local deformation energy with respect to graphene, which we determine by estimating the two principal radii of curvature at each lattice site using the Bertrand-Diquet-Puiseux theorem. We find an impressive level of agreement between strain energies based on local curvature and ab initio density functional calculations. We demonstrate that our approach correctly determines strain energy differences between nanotubes with different chiral indices (n,m) and zero Gaussian curvature, C n fullerenes with 20≤n≤72 atoms and positive Gaussian curvature, and selected schwarzites with negative Gaussian curvature. In contrast to other methods, our approach correctly determines even the energy differences between different isomers of fullerenes such as C 28 , C 36 and C 38 .
Bulletin of the American Physical Society, 2005
ABSTRACT
Bulletin of the American Physical Society, 2007
We investigate the effect of atomic ordering and geometry on the relative stability and electroni... more We investigate the effect of atomic ordering and geometry on the relative stability and electronic as well as magnetic structure of Mo6S9-xIx nanowires using ab initio Spin Density Functional calculations. The skeleton of these unusually stable nanowires consists of Mo octahedra, which are decorated with S and I atoms and connected by sulfur bridges. These sulfur bridges turn out to be bi-stable, providing the nanowires with the unusual capability to stretch by 20% at no energy cost. Depending on the degree the nanowires have been stretched, they may reversibly acquire or lose their magnetic moment. The ordering of the decorating atoms, observed in these nanowires, reflects our finding that the total energy depends sensitively on the atomic arrangement at a given stoichiometry.
Physics Letters A, 1986
Abstract A simple criterion is introduced which allows one to estimate the tendency of metal surf... more Abstract A simple criterion is introduced which allows one to estimate the tendency of metal surfaces to reconstruct. At clean surfaces changes in surface tension γ 0 are estimated from a simple formula based on a tight-binding hamiltonian, yielding surface multilayer relaxations as by-product. The effect of adsorbates to induce or to suppress reconstruction is described by adsorbate-dependent modifications of γ 0 . The calculation successfully describes reconstruction at clean and adsorbate-covered (110) and (100) surfaces of Ir, Pt and Au.
Physical Review Letters, 2011
Physical Review Letters, 2012
We use ab initio density functional calculations to study the formation and structural as well as... more We use ab initio density functional calculations to study the formation and structural as well as thermal stability of cellular foam-like carbon nanostructures. These systems with a mixed sp 2 /sp 3 bonding character may be viewed as bundles of carbon nanotubes fused to a rigid contiguous 3D honeycomb structure that can be compressed more easily by reducing the symmetry of the honeycombs. The foam may accommodate the same type of defects as graphene, and its surface may be be stabilized by terminating caps. We postulate that the foam may form under non-equilibrium conditions near grain boundaries of a carbon-saturated metal surface.
Physical Review Letters, 2004
We propose a new microscopic mechanism to explain the unusually fast fusion process of carbon nan... more We propose a new microscopic mechanism to explain the unusually fast fusion process of carbon nanotubes. We identify the detailed pathway for two adjacent (5,5) nanotubes to gradually merge into a (10,10) tube, and characterize the transition states. The propagation of the fused region is energetically favorable and proceeds in a morphology reminiscent of a Y junction via a zipper mechanism, involving only Stone-Wales bond rearrangements with low activation barriers. The zipper mechanism of fusion is supported by a time series of high-resolution transmission electron microscopy observations.
Angewandte Chemie, 2013
ABSTRACT Diamant‐Nanodrähte bilden sich innerhalb von Kohlenstoff‐Nanoröhren durch Tempern von Di... more ABSTRACT Diamant‐Nanodrähte bilden sich innerhalb von Kohlenstoff‐Nanoröhren durch Tempern von Diamantan‐4,9‐dicarbonsäure in einer Wasserstoffatmosphäre. H. Shinohara et al. beschreiben in der Zuschrift auf S. 3805 ff. die Synthese und den Nachweis dieser Nanodrähte. Das Bild zeigt das Eintragen von Diamantan‐4,9‐dicarbonsäure in doppelwandige Kohlenstoff‐Nanoröhren mit offenen Enden, das Tempern unter Wasserstoff (roter “Rauch”) und die Umwandlung in Diamant‐Nanodrähte (goldene Strukturen).
Alkali metal adducts to LOGEAs (Large Organic Globular Electron Acceptors) share with superconduc... more Alkali metal adducts to LOGEAs (Large Organic Globular Electron Acceptors) share with superconducting `Buckyball` adducts such as K3C60 the globular shape, delocalized pi systems and accessible reduction potentials that are believed important for superconductivity. This research focused on the synthesis and study of reduced macrobicyclic Schiff-base cryptands that have an aromatic linking group in each of the three strands. Some samples, when reduced with Rb or K, showed LFMA (Low Frequency Microwave Absorption) up to 50 K and/or a pronounced diamagnetic downturn in the susceptibility below 30 K. These phenomena are usually associated with superconductivity. The magnitude of these effects was, however, only that expected for traces (<1%) of superconducting phases and the effects were only present in a few samples. Much effort over a two-year time span was directed toward the identification and isolation of the phase(s) responsible, but without success. Although superconductivity could not be verified, these studies opened a new area of research; the study of the solid state behavior of radical anion salts. Except for some crystal structure determinations, this field is virtually unexplored and is likely to lead to potentially useful electronic and magnetic materials. The stability at and above room temperature, even of multiply reduced compounds, is especially encouraging.
FIG.1. Calculated electron density difference ∆ρ=ρtot(bulk)−Σρtot(monolayers) representing the ch... more FIG.1. Calculated electron density difference ∆ρ=ρtot(bulk)−Σρtot(monolayers) representing the charge redistribution caused by assembling the bulk structure from isolated monolayers. (a) Diffusion Monte Carlo (DMC) isosurfaces bounding regions of excess electron density (dark brown) and electron deficiency (light brown), with respective values ±6.5×10 e/Å. (b) <∆ρ(z)> for DMC and selected DFT functionals averaged across the x−y plane of the layers, with z/c indicating the relative position of the plane in the unit cell. (From Ref. [3]). If graphene had a band gap, it would probably be the optimum 2D system for electronics applications. Layered transition metal dichalcogenides (TMDs) with a robust intrinsic band gap appear as the next-best alternative. Only after a long search, however, optimum strategies have been devised to make low-resistance, ohmic contacts to TMDs [1]. In the meantime, a new class of 2D semiconductors has been rapidly gaining attention, namely layered blac...
The mechanical response of carbon nanotubes to revere deformation has attracted much attention si... more The mechanical response of carbon nanotubes to revere deformation has attracted much attention since their discovery in 1991. Carbon nanotubes have already demonstrated exceptional mechanical properties: their excellent flexibility during bending have been observed experimentally. Nanotubes combine high stiffness with elasticity and the ability to buckle and collapse in a reversible manner even largely axially compressed or twisted deformation. For these reasons, it has been suggested that carbon nanotubes could be promising candidates for a new generation of extremely light and super strong fiver. However, experiments probing the strength of nanotubes are very challenging, but to the difficulties in growing high quality, defect-free nanotubes of sufficient length and in measuring the strength of nanoscale objects. Theoretically, investigating the strength of carbon nanotubes requires modeling of inherently mesoscopic phenomena, such as plasticity and fracture on a microscopic compo...
The unique electronic transport behavior of quasi-1D carbon nanotubes(Stefano Sanvito, Young-Kyun... more The unique electronic transport behavior of quasi-1D carbon nanotubes(Stefano Sanvito, Young-Kyun Kwon, David Tomanek, and Colin J. Lambert, Phys. Rev. Lett. 84), 1974 (2000). finds an unexpected counterpart in their unusually high thermal conductance.(Savas Berber, Young-Kyun Kwon, and David Tomanek, Phys. Rev. Lett. 84), 4613 (2000). The latter is a consequence of the structural rigidity of nanotubes, resulting in a large sound velocity, and their phonon structure. Soft phonon modes, primarily associated with tube bending and twisting, are essentially decoupled from the energy-carrying hard phonon modes which originate in the stretching and bending of interatomic bonds. The absence of an efficient coupling mechanism between these different phonon modes is responsible for their low damping and a long phonon mean free path. With a peak value lambda=37,000W/m/K at 100K, the thermal conductance of an isolated (10,10) nanotube, predicted using non-equilibrium molecular dynamics simulations, is comparable to that of isotopically pure diamond. At room temperature, the predicted value lambda=6,600W/m/K even exceeds that of this best thermal conductor. Unlike bulk graphite, where coupling between the flexible layers reduces the basal plane thermal conductance by one order of magnitude, we find that the inter-tube coupling in nanotube ropes does not reduce the single-tube conductance significantly.
Bulletin of the American Physical Society, 2014
A study of the electronic structure of carbon nanoparticles has been carried out using the method... more A study of the electronic structure of carbon nanoparticles has been carried out using the methods of quantum chemistry and X-ray emission spectroscopy. Fragments of (n, 0) tubes with n = 6, ... ,11 and of (5,5)-(10,0) tubes were calculated using PM3 method. The dependence of the electronic structure of the fragment on length and symmetry was investigated. The structure of the frontier orbitals was shown to change regularly depending on the tube chirality. Band structure of (n,O) and (5,5) tubes was studied by the tight-binding method. A comparison of the basic blocks of the molecular orbitals (MOs) of the fragment and bands of (6,0) and (5,5) tubes was carried out. Experimental CKo spectra. for single-wall and multiwall carbon nanotubules were obtained. These spectra agree satisfactorily with the theoretical spectra plotted as the results of cluster calculations. The structure of the valence zone for the central hexagons of the nanotube fragments keeps the basic features in the ser...