Showing papers by "Roberto Car published in 1990"

Ab initio calculation of properties of carbon in the amorphous and liquid states

Abstract: We have carried out a detailed investigation of liquid carbon (l-C) at T\ensuremath{\simeq}5000 K, and quenched amorphous carbon (a-C) at room temperature, using a first-principles molecular-dynamics method. In this paper we report calculations performed for a fixed density corresponding to low pressures. From our results, which agree well with the limited experimental information available, we analyze the short-range order, particularly the fractions of sp, ${\mathit{sp}}^{2}$, and ${\mathit{sp}}^{3}$ sites, and the electronic properties of the two systems. In addition, we discuss new features of a-C and l-C, predicted by our calculation, and present an analysis of some models proposed in the literature to account for their electronic and bonding properties, as well as of recent controversial experiments.

Structural, electronic, and vibrational properties of Si(111)-2 x 1 from ab initio molecular dynamics.

Abstract: Our findings for the equilibrium structure confirm the Pandey (2 × 1) chain model and are in very good agreement with both LEED and medium-energy ion-scattering data, showing in particular a large buckling of the surface chains. We describe the dynamical path followed during the reconstruction from the ideal bulk-terminated surface, which is found to be unstable. The phonon spectrum, which is calculated ab initio for the first time, shows well-defined surface modes at frequencies close to the measured values

Melting of diamond at high pressure.

Abstract: Melting of diamond at high pressure and the properties of liquid carbon at pressures greater than 1 megabar were investigated with a first-principles molecular dynamics technique. The results indicate an increase of the diamond melting temperature with pressure, which is opposite to the behavior of silicon and germanium. This is contrary to long-held assumptions, but agrees with recent experiments, and has important implications for geology and astrophysics. As is the case for the solid phase of carbon at low temperature, which changes greatly with pressure from graphite to diamond, the structural and bonding properties of liquid carbon vary strongly with pressure.

Atomic structure and bonding in liquid GaAs from Iab-initioP molecular dynamics

Abstract: The structural and electronic properties of liquid GaAs are investigated using ab initio molecular-dynamics methods. In agreement with experiments, we find that liquid GaAs is metallic, with an average coordination number between 5 and 6. Analysis of the electronic-charge distribution shows that weakly ionic bonds, similar to those of crystalline GaAs, are still present in the liquid. At variance with the crystal, these bonds are not permanent, but are continuously formed and disrupted by atomic diffusion. On the average, however, almost 50% of the atoms of the first coordination shell are bonded to the central atom. Bonds between like atoms are very frequent (\ensuremath{\sim}27%); three-atom clusters of a single species have a relative probability of 6%, while larger clusters occur only occasionally.

Thermal expansion of c-Si via ab initio molecular dynamics

Abstract: On montre que les proprietes thermodynamiques des semiconducteurs sont accessibles aux calculs des premiers principes et peuvent etre calculees avec une grande exactitude

Liquid arsenic: Comparison of ab initio and pair-potential predictions of molecular structure.

Abstract: Les fonctions de distribution radiale obtenues par ces deux procedures sont coherentes avec l'experience. On predit que la coordination evolue du seuil au degre six quand on augmente la densite

Atomic structure and bonding in liquid GaAs

Abstract: Liquid GaAs is investigated using ab-initio molecular dynamics methods. From our results, which are in good agreement with the available experimental information, we obtain a detailed picture of the atomic and electronic structure of the liquid.