Showing papers by "Roberto Car published in 2002"
TL;DR: By comparing classical and quantum Monte Carlo annealing protocols on the two-dimensional random Ising model (a prototype spin glass), this work confirms the superiority of quantumAnnealing relative to classical annealed and proposes a theory of quantum annealer based on a cascade of Landau-Zener tunneling events.
Abstract: Probing the lowest energy configuration of a complex system by quantum annealing was recently found to be more effective than its classical, thermal counterpart. By comparing classical and quantum Monte Carlo annealing protocols on the two-dimensional random Ising model (a prototype spin glass), we confirm the superiority of quantum annealing relative to classical annealing. We also propose a theory of quantum annealing based on a cascade of Landau-Zener tunneling events. For both classical and quantum annealing, the residual energy after annealing is inversely proportional to a power of the logarithm of the annealing time, but the quantum case has a larger power that makes it faster.
703 citations
TL;DR: In this article, the authors report an extensive ab initio study of self-interstitials in V and Mo. Contrary to the widely accepted picture, the $〈111〉$ dumbbell is found to be the most stable structure.
Abstract: We report an extensive ab initio study of self-interstitials in V and Mo. Contrary to the widely accepted picture, the $〈111〉$ dumbbell is found to be the most stable structure. The activated state for migration is the crowdion configuration, with an extremely low barrier $(\ensuremath{\sim}0.01\mathrm{eV}),$ suggesting $1d$ (one-dimensional) diffusion at low temperatures and $3d$ diffusion at high temperature. In the case of Mo, the energy landscape between the $〈111〉$ and $〈110〉$ dumbbells is very shallow. Predicted migration energies and self-interstitial structures are consistent with experiment.
110 citations
TL;DR: First-principles molecular dynamics simulations at constant pressure have been used to investigate the mechanisms of compression of liquid SiO2 and are found to become denser than quartz at a pressure of about 6 GPa, in agreement with extrapolations of lower pressure experimental data.
Abstract: First-principles molecular dynamics simulations at constant pressure have been used to investigate the mechanisms of compression of liquid SiO2. Liquid SiO2 is found to become denser than quartz at a pressure of about 6 GPa, in agreement with extrapolations of lower pressure experimental data. The high compressibility of the liquid is traced to medium-range changes in the topology of the atomic network. These changes consist in an increase of network connectivity caused by the pressure-induced appearance of coordination defects.
93 citations
TL;DR: The density functional theory (DFT) has been used extensively for electronic structure analysis in condensed phase and complex molecular environments as discussed by the authors, and is the method of choice for first-principles electronic structure calculations.
Abstract: Density-Functional-Theory (DFT) provides a general framework to deal with the ground-state energy of the electrons in many-atom systems. Its history dates back to the work of Thomas [1], Fermi [2] and Dirac [3] who devised approximate expressions for the kinetic energy [1, 2] and the exchange energy [3] of many-electron systems in terms of simple functionals of the local electron density. These ideas were further elaborated in the Xα method of Slater [4], until finally, the foundations of the modern theory were laid down in the mid-sixties by Kohn and collaborators [5, 6]. Since then but particularly in the last two decades the number of applications of DFT to electronic structure problems has grown dramatically. Today DFT is the method of choice for first-principles electronic structure calculations in condensed phase and complex molecular environments. DFT based approaches are used in a variety of disciplines ranging from condensed matter physics, to chemistry, materials science, biochemistry and biophysics. There are several reason for this success: (i) DFT makes the many-body electronic problem tractable at a numerical cost of self-consistent-field single particle calculations; (ii) despite the severe approximations made to the exchange and correlation energy functional, DFT calculations are usually sufficiently accurate to predict materials structures or chemical reactions products; (iii) currently available computational power and modern numerical algorithms make DFT calculations feasible for realistic models of systems like e.g. an interface between two crystalline materials, a carbon nanotube, or the active site of an enzyme.
46 citations
TL;DR: In this paper, the interaction of Ti atoms with thin films made of 3,4,9,10 perylenetetricarboxylic dianhydride (PTCDA) molecules was investigated by means of self-consistent electronic structure calculations within a generalized gradient approximated density-functional theory framework.
Abstract: We investigate the interaction of Ti atoms with thin films made of 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA) molecules by means of self-consistent electronic structure calculations within a generalized gradient approximated density-functional theory framework Following experimental suggestions, we model the thin films in terms of the bulk crystallographic structure of PTCDA We fully optimize the atomic PTCDA structures in the presence of Ti impurities by local minimizations of the electronic total energy We find that the Ti atoms react with the anhydride groups of PTCDA and form additional bridge-type bonds with the surrounding molecules This process is accompanied by an electronic charge transfer from the metal atoms to the organic molecules, which provides a consistent interpretation of the experimentally observed C 1s core-level shifts upon metal deposition As a consequence of the chemical reaction, electronic states are induced in the gap above the highest occupied molecular orbital level of the organic semiconductor, in good agreement with photoemisssion studies
24 citations
TL;DR: In this paper, a tetrahedral water model was proposed for the Pt(111) surface, which is the only face of Pt that exhibits a clear first order phase transition and showed that the water molecules in the inner Helmholtz layer are strongly oriented by the field.
19 citations
TL;DR: In this article, the authors present first-principle total energy calculations of carbon incorporation in the hydrogen-saturated Si(100)2H-1 X I surface and a large variety of atomic configurations involving one, two, and four substitional C impurities in surface and subsurface sites.
Abstract: We present first-principle total-energy calculations of carbon incorporation in the hydrogen-saturated Si( 100)2H-1 X I surface. A large variety of atomic configurations involving one, two, and four substitional C impurities in surface and subsurface sites is considered. While carbon incorporation in the surface layer is energetically favored, C-C interactions play an important role and can stabilize configurations that would be otherwise unlikely, particularly configurations with carbon atoms in the 5th layer, as observed in recent x-ray photoelectron-spectroscopy experiments.
4 citations
01 Jan 2002
TL;DR: In this article, the authors present an overview of the relationship between physics, chemistry, and physics in the field of physics and chemistry. But they do not discuss the relationships between the two domains.
Abstract: 1 Unité de Physico-Chimie et de Physique des Matériaux, Université Catholique de Louvain, Place Croix du Sud 1, B-1348 Louvain-la-Neuve, Belgium. 2 Département de Physique des Matériaux, U.M.R. n° 5586, Université Claude Bernard, 43 bd. du 11 Novembre 1918, F-69622 Villeurbanne Cedex, France. 3 Istituto Nazionale di Fisica della Materia (INFM) and Department of Material Engineering and Applied Chemistry, University of Trieste, via Valerio 2, I-34149 Trieste, Italy. 4 Institut Romand de Recherche Numérique en Physique des Matériaux, PPH-Ecublens, CH-1015 Lausanne, Switzerland. 5 Department of Chemistry and Princeton Materials Institute, Princeton University, Princeton, New Jersey 08544, USA.
1 citations