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Showing papers by "Roberto Car published in 1993"


Journal ArticleDOI
TL;DR: It is shown how the ultrasoft pseudopotentials which have recently been proposed by Vanderbilt can be implemented efficiently in the context of Car-Parrinello molecular-dynamics simulations.
Abstract: We show how the ultrasoft pseudopotentials which have recently been proposed by Vanderbilt can be implemented efficiently in the context of Car-Parrinello molecular-dynamics simulations We address the differences with respect to the conventional norm-conserving schemes, identify certain problems which arise, and indicate how these problems can be overcome This scheme extends the possibility of performing first-principles molecular dynamics to systems including first-row elements and transition metals

1,106 citations


Journal ArticleDOI
TL;DR: An ab initio molecular dynamics simulation of liquid water has been performed using density functional theory in the Kohn-Sham formulation and a plane wave basis set to determine the electronic structure and the forces at each time step.
Abstract: An ab initio molecular dynamics simulation of liquid water has been performed using density functional theory in the Kohn–Sham formulation and a plane wave basis set to determine the electronic structure and the forces at each time step. For an accurate description of the hydrogen bonding in the liquid, it was necessary to extend the exchange functional with a term that depends on the gradient of the electron density. A further important technical detail is that supersoft pseudopotentials were used to treat the valence orbitals of the oxygen atoms in a plane wave expansion. The structural and dynamical properties of the liquid were found to be in good agreement with experiment. The ab initio molecular dynamics also yields information on the electronic structure. The electronic feature of special interest is the lowest unoccupied molecular orbital (LUMO) of the liquid which is the state occupied by a thermalized excess electron in the conductive state. The main result of calculating the liquid LUMO is that it is a delocalized state distributed over interstitial space between the molecules with a significant admixture of the σ* orbitals of the individual water molecules.

573 citations


Journal ArticleDOI
TL;DR: A novel energy functional for total-energy and molecular-dynamics calculations is introduced, and proven to have the Kohn-Sham ground-state energy as its absolute minimum, which leads to an algorithm for electronic structure calculations whose computational work load grows linearly with the system size.
Abstract: A novel energy functional for total-energy and molecular-dynamics calculations is introduced, and proven to have the Kohn-Sham ground-state energy as its absolute minimum. The use of this functional within a localized orbital formulation leads to an algorithm for electronic structure calculations whose computational work load grows linearly with the system size. The foundations and accuracy of the approach and the performances of the algorithm are first discussed analytically and then illustrated with several numerical examples.

341 citations


Journal ArticleDOI
TL;DR: The first parameter-free calculations of self-diffusion constants in silicon are reported, with the self-interstitial mechanism dominating over the contribution of the other mechanisms.
Abstract: We report the first parameter-free calculations of self-diffusion constants in silicon. We have computed diffusion constants for the defect-mediated mechanisms using the local-density approximation in combination with ab initio molecular-dynamics simulations and obtained the diffusion constant for the concerted exchange mechanism from earlier results by Pandey and Kaxiras. We obtain diffusion constants in the range of the experimental values, with the self-interstitial mechanism dominating over the contribution of the other mechanisms.

205 citations


Journal ArticleDOI
TL;DR: In this article, the structures of small water clusters (up to 8 molecules) have been studied using gradient-corrected density functional theory and ab initio molecular dynamics, and for smaller clusters (3, 4 and 6 molecules) ring structures were found to be the most stable.

175 citations


Journal ArticleDOI
TL;DR: The structural and dynamical properties of cubic H 2 O and D 2 O ice phases are studied using ab initio molecular dynamics combined with ultrasoft pseudopotentials and the agreement with the experimental data is reasonable and the isotope effects are well reproduced.
Abstract: The structural and dynamical properties of cubic ${\mathrm{H}}_{2}$O and ${\mathrm{D}}_{2}$O ice phases are studied using ab initio molecular dynamics combined with ultrasoft pseudopotentials. Phonon frequencies are extracted from the velocity autocorrelation functions; contributions from different normal modes in the phonon spectra are separated and easily identified. For the low-pressure phases, the agreement with the experimental data is reasonable and the isotope effects are well reproduced. High-pressure phases are also studied. The equations of state for cubic ice (ice ${\mathrm{I}}_{\mathit{c}}$), and for the ice VII-VIII-X family, are calculated. It is found that the local-density approximation must be augmented with gradient corrections in order to obtain a proper description of the hydrogen bond. Finally, the hydrogen-bond symmetrization, which is responsible for the transition from ice VII-VIII to ice X, is studied and is predicted to occur at 49 GPa. The nature of the phase transition is found to be that of a mode-softening transition. The corresponding symmetrization is also studied in ice ${\mathrm{I}}_{\mathit{c}}$, but it is found to occur at a pressure of 7 GPa at which ice ${\mathrm{I}}_{\mathit{c}}$ is unstable with respect to denser phases.

147 citations


Journal ArticleDOI
TL;DR: Analysis of the energetics of adsorption and the mobility of Al adatoms reveals that the long, one-dimensional strings of Al dimers observed experimentally result from a sequence of reaction steps which can be classified as a surface polymerization.
Abstract: We study the adsorption of Al on the Si(100) surface by ab initio calculations for a complete range of coverages from an isolated Al adatom up to full surface coverage. Analysis of the energetics of adsorption and the mobility of Al adatoms reveals that the long, one-dimensional strings of Al dimers observed experimentally result from a sequence of reaction steps which can be classified as a surface polymerization. The calculated local density of states (LDOS) of the adsorbed Al row is compared with scanning tunneling microscopy images. The LDOS characteristic of the reaction sites which mediate the polymerization should be observable by scanning tunneling spectroscopy.

113 citations


Journal ArticleDOI
20 Nov 1993-EPL
TL;DR: In this paper, the thermal-equilibrium distribution generated by a Nose-Hoover thermostat coupled to a mixed quantum-classical system, whose time evolution is taken to be either Ehrenfest (E), or Car-Parrinello (CP) type, is studied.
Abstract: We study the thermal-equilibrium distribution generated by a Nose-Hoover thermostat coupled to a mixed quantum-classical system, whose time evolution is taken to be either Ehrenfest (E), or Car-Parrinello (CP) type. It is found that neither E or CP dynamics lead to the correct averages for the quantum subsystem. A new classical modified CP dynamics is introduced which mimics the level quantization and yield the correct quantum averages after a suitable reweighting of the trajectories. We support our theoretical formulation with numerical simulations on a simple model system.

35 citations


Journal ArticleDOI
TL;DR: In this article, the Car-Parrinello ab initio molecular dynamics scheme was applied to organic semiconducting polymers and the bandgaps of these polymers, calculated with the local density functional, correctly represent the trend in the experimental optical bandgap.

33 citations


Journal ArticleDOI
TL;DR: The calculated structure factors and local density of states agree well with x-ray diffraction and STM data and fluctuations are found to disrupt long-range Pb chains and restore the threefold symmetry of the ideal Ge(111) surface.
Abstract: We have studied the low temperature phases of Pb/Ge(111) at Pb coverages Θ=1/3, 1, and 4/3 using ab initio molecular dynamics. Stable phases are found to occur at Θ=1/3 and 4/3. For the low-coverage (Θ=1/3) α phase, we confirm the model of Pb atoms adsorbed at T4 sites of the Ge(111) substrate. For the high coverage (Θ=4/3) β phase and very low temperature, we determine a structure characterized by the presence of covalently bonded Pb chains parallel to 〈11¯0〉 substrate directions. At room temperature, fluctuations are found to disrupt long-range Pb chains and restore the threefold symmetry of the ideal Ge(111) surface. The calculated structure factors and local density of states agree well with x-ray diffraction and STM data.

15 citations