Showing papers by "Roberto Car published in 1995"
TL;DR: On the basis of the partial structure factors, the origin of the first sharp diffraction peak is investigated and affects differently the localization properties of valence and conduction band states, as suggested by experimental mobilities of electrons and holes.
Abstract: We performed a first-principles molecular dynamics study of liquid ${\mathrm{SiO}}_{2}$ at a temperature of 3500 K, followed by a rapid quench to 300 K obtaining a perfectly chemically ordered amorphous network. Structural and electronic properties of our amorphous sample are in good agreement with neutron diffraction, x-ray photoemission, and optical experiments. On the basis of the partial structure factors, we investigated the origin of the first sharp diffraction peak. Disorder affects differently the localization properties of valence and conduction band states, as suggested by experimental mobilities of electrons and holes.
206 citations
TL;DR: It is shown that properties like the specific entropy, the specific volume, or the heat capacity of a solid and a liquid can be calculated accurately and this greatly extends the range of first-principles predictions of materials properties.
Abstract: We present a scheme to compute the thermodynamic properties and the phase stability of materials based on parameter-free microscopic quantum theory Taking silicon as an example we show that properties like the specific entropy, the specific volume, or the heat capacity of a solid and a liquid can be calculated accurately In particular, we can locate the solid-liquid phase boundary and compute how thermodynamic properties change upon melting This greatly extends the range of first-principles predictions of materials properties
182 citations
TL;DR: In this paper, the core-hole relaxation between Si and tridymite, a crystalline form of Si${\mathrm{O}}_{2}, was investigated and the results showed a linear dependence on the number of nearest-neighbor oxygen atoms.
Abstract: Using a first-principles approach, we calculate core-level shifts at the Si(001)-Si${\mathrm{O}}_{2}$ interface. By fully relaxing interfaces between Si and tridymite, a crystalline form of Si${\mathrm{O}}_{2}$, we obtain interface models with good local structural properties and with no electronic states in the Si gap. Calculated values of Si $2p$ core-level shifts agree well with data from photoemission experiments and show a linear dependence on the number of nearest-neighbor oxygen atoms. Core-hole relaxation accounts for \ensuremath{\sim}50% of the total shifts, in good agreement with Auger experiments.
156 citations
TL;DR: Structural and electronic properties of the model glass present a remarkable agreement with vitreous SiO2: the calculated total structure factor closely agrees with data from neutron diffraction experiments and features in the x-ray photoemission spectrum are well reproduced by the electronic density of states.
Abstract: We studied liquid and vitreous SiO2 by performing first-principles molecular-dynamics simulations. Diffusion in the liquid is shown to occur through correlated jump events, which disrupt the network only for short time periods. The persistence of the network even at high temperatures is confirmed by the average structural properties of the liquid. By quenching from the melt, we obtained a model for the glass, which forms a perfectly chemically ordered network. Structural and electronic properties of our model glass present a remarkable agreement with vitreous SiO2: the calculated total structure factor closely agrees with data from neutron diffraction experiments and features in the x-ray photoemission spectrum are well reproduced by the electronic density of states. This agreement strongly supports other structural properties which are yet unavailable from experiment such as partial pair correlation functions and bond-angle distributions. A comparative study of the electronic density of states in liquid, vitreous, and crystalline SiO2 shows that enhancement of disorder gives rise to a reduction of the gap.
156 citations
TL;DR: In this paper, equilibrium geometries and electronic properties of neutral Cun (n = 2, 3, 4, 6, 8, 10) clusters are determined via first principles calculations which treat s and d electrons on an equal footing.
81 citations
TL;DR: This calculation provides evidence for self-trapping of the core exciton and gives a coherent interpretation of recent experimental x-ray absorption and emission data, predicting that self-Trapping should occur in the case of a valence biexciton.
Abstract: We present a first-principles study of excitonic self-trapping in diamond. Our calculation provides evidence for self-trapping of the core exciton and gives a coherent interpretation of recent experimental x-ray absorption and emission data. Self-trapping does not occur in the case of a single valence exciton. We predict, however, that self-trapping should occur in the case of a valence biexciton. This process is accompanied by a large local relaxation of the lattice which could be observed experimentally.
55 citations
TL;DR: Equilibrium geometries and electronic properties of neutral and anionic Cu-n (n = 2,9) clusters are determined by means of first principles calculations in which s and d electrons are treated on equal footing.
Abstract: We have determined equilibrium geometries and electronic properties of neutral and anionic Cu-n (n = 2,9) clusters by means of first principles calculations in which s and d electrons are treated on equal footing. We find that the calculated electronic density of states is inadequate to interpret photoelectron spectra of Cu-n(-) clusters. We obtain good agreement between calculated excitation energies and experimental spectra when we include final states effects.
45 citations