Showing papers by "Roberto Car published in 1989"
TL;DR: A new robust iterative method based on a convenient adaptation of the conjugate gradient minimization of the energy functional is presented, showing to be rapidly convergent, irrespective of the system under consideration, thus providing an efficient solution to a variety of large-scale electronic structure calculations.
Abstract: A new robust iterative method for electronic structure calculations based on a convenient adaptation of the conjugate gradient minimization of the energy functional is presented. The method is compared with some other techniques using the direct minimization of the density functional and with a more traditional Davidson approach. Numerical results for silicon and carbon are used to compare the different schemes. The new method is shown to be rapidly convergent, irrespective of the system under consideration, thus providing an efficient solution to a variety of large-scale electronic structure calculations.
298 citations
TL;DR: Determination de the structure amorphe par simulation sur ordinateur basee sur une methode de dynamique moleculaire aux premiers principes.
Abstract: An amorphous carbon structure is obtained with a computer simulation based on a first-principles molecular-dynamics method, in which the interatomic potential is constructed directly from the electronic ground state, using density-functional techniques. From our results, which agree well with the limited experimental information available, we analyze the short-range order, particularly the fractions of $s{p}^{2}$ and $s{p}^{3}$ sites, together with the electronic properties.
233 citations
TL;DR: Les densites d'etats electroniques illustrent un comportement metallique and les valeurs calculees pour the conductivite electronique correspondent parfaitement aux donnees experimentales.
Abstract: Etude du silicium liquide selon les premiers principes de la dynamique moleculaire. La description de l'ordre local est en plein accord avec les resultats obtenus par diffraction de RX et de neutrons. La densite de charge electronique met en evidence des liaisons de covalence distinctement identifiables dans le spectre de puissance du systeme. Les densites d'etats electroniques illustrent un comportement metallique et les valeurs calculees pour la conductivite electronique correspondent parfaitement aux donnees experimentales
188 citations
TL;DR: In this paper, a new method for the simulation of ground-state properties of interacting fermions is introduced, where a trial wave function, which is assumed to be a Slater determinant, is propagated to large imaginary times.
Abstract: A new method for the simulation of ground-state properties of interacting fermions is introduced. A trial wave function, which is assumed to be a Slater determinant, is propagated to large imaginary times. The quantum many-body propagator is represented by a coherent superposition of single-particle propagators by means of a Hubbard-Stratonovich transformation. The resulting functional integral is performed by stochastic methods based on Langevin dynamics. Numerical stability is achieved by orthonormalizing the propagating single-particle orbitals entering the Slater determinant. The problem of the positiveness of the statistical weight is addressed and solved in most cases. Illustrative examples are given for the 1D and 2D Hubbard models.
175 citations
TL;DR: An ab initio molecular-dynamics simulation of high-temperature proton diffusion in crystalline silicon finds that the diffusion proceeds via a jumplike mechanism.
Abstract: An ab initio molecular dynamics simulation of high-temperature proton diffusion in crystalline silicon is presented. This is the first time dynamical effects have been included explicitly in the simulation of this system. We find that the diffusion proceeds via a jumplike mechanism. Because of dynamical effects the diffusion path is substantially different from that inferred from static total-energy calculations. The calculated diffusion coefficient and its temperature dependencne are in good agreement with the available experimental data. It is suggested that scattering experiments may distinguish between different diffusion paths.
116 citations
TL;DR: The liquid state of carbon at low pressure is investigated in terms of density of states and conductivity calculations, showing that the system is a metal, in agreement with experiments reported last year.
Abstract: The liquid state of carbon at low pressure is investigated wtih a first-principles molecular dynamics simulation. Its controversial electronic properties are elucidated in terms of density of states and conductivity calculations, showing that the system is a metal, in agreement with experiments reported last year. Furthermore, an accurate analysis of the atomic structure indicates that the liquid is composed of two-fold, three-fold, and four-fold coordinated atoms, which display different bonding properties.
87 citations
TL;DR: In this paper, an ab initio molecular dynamics study of the ground state, finite temperature, dynamical and electronic properties of Na20 and Na10K10 microclusters is presented.
Abstract: We present an ab initio molecular dynamics study of the ground state, finite temperature, dynamical and electronic properties of Na20 and Na10K10 microclusters. For Na20 the lowest-energy structure has several bulklike features. The vibrational spectrum at 200 K is compared to that of the liquid. From our results we derive a rationale for the so far unexplained dependence of the mass spectrum on the nozzle temperature and compositional abundance of the mixed clusters. The implications of our calculations on the validity of the shell model are discussed in detail.
61 citations
25 citations
TL;DR: In this article, the interatomic potential of Si, both elemental and hydrogenated, is derived from the electronic ground-state of the semiconductor and the numerical results can be directly compared with several experimental data.
Abstract: Several applications have demonstrated that a recently developed first-principles molecular dynamics method allows to predict structural, dynamical and electronic properties of non-crystalline semiconductors. In this scheme the interatomic potential is explicitely derived from the electronic ground-state. Here we discuss in particular the case of Si , both elemental and hydrogenated. The numerical results can be directly compared with several experimental data. In addition, they reveal details of the microscopic dynamics that are not directly accessible to experiment and provide insight into the bonding mechanisms that lead to the formation of the disordered structures.
16 citations
TL;DR: In this article, a new method for simulating strongly correlated fermionic systems has been applied to the study of the ground state properties of the 2D Hubbard model at various fillings.
Abstract: A new method for simulating strongly correlated fermionic systems has been applied to the study of the ground state properties of the 2D Hubbard model at various fillings. Comparison has been made with exact diagonalization in the 2×2, 3×3 and 4×4 lattices where very good agreement has been verified. Numerical results concerning a)magnetization, b)momentum distribution, c)charge, spin and pairing correlations have been obtained with this method for sizes up to 16×16 sites and several fillings. The 2D antiferromangetic order is destroyed by the presence of few holes and is very sensitive to the boundary conditions. The momentum distribution of the doped system does not have a clear Fermi surface. This is also supported by the exponential decay of the density matrix at large enough distances. Particular attention will be paid to the single hole properties and hole-hole correlations.
13 citations
TL;DR: In this paper, an approach that uses a local spin density description of many electron interactions, is a powerful and efficient method for the study of the adiabatic dynamics of such systems.
Abstract: Metal molten salt solutions exhibit a number of interesting properties with variation of the metal concentration. In the dilute limit, the metal valence electrons are released to form F-center-like localized states. At higher concentrations, metallic behavior sets in. A theoretical approach to the properties of these systems obviously requires a correct quantum-mechanical treatment of the solvated electrons. We show here that an approach that uses a local spin density description of many electron interactions, is a powerful and efficient method for the study of the adiabatic dynamics of such systems. We apply our approach to the case of one and two solvated electrons. In the first case we confirm the F-center model and elucidate the mechanism of electron diffusion. In the case of two solvated electrons, we find that parallel spin electrons repel each other and form separate F-center-like states. Antiparallel spin electrons, instead, attract each other and coalesce into a single bipolaronic complex. The diffusion of the bipolaron, while bound, occurs on a ionic time scale. However, dissociation process occur during which the electrons can acquire a high mobility leading to a large electronic diffusion. At even higher concentrations preliminary indication of clustering and of metallic behavior are observed.
01 Jan 1989
TL;DR: In this article, the authors present some very recent results on small semiconductor aggregates with special reference to calculations of equilibrium shapes and temperature effects, as well as results of simulations on alkali-metal microclusters.
Abstract: The study of the structural and electronic properties of microclusters is a field of growing interest. Ab-initio molecular dynamics has provided a new and important tool for the theoretical approach to these questions. Here we present some very recent results on small semiconductor aggregates with special reference to calculations of equilibrium shapes and temperature effects. Results of simulations on alkali-metal microclusters are briefly mentioned.
TL;DR: In this article, the static and dynamic properties of hydrogen in crystalline and amorphous silicon were investigated by means of ab initio molecular dynamics simulations, focusing mainly on the diffusion process of an isolated positively charged hydrogen impurity at high temperature.
Abstract: We investigate static and dynamic properties of hydrogen in crystalline and amorphous silicon by means of ab initio molecular dynamics simulations. In the crystalline case we focus mainly on the diffusion process of an isolated positively charged hydrogen impurity at high temperature. In the amorphous case we analyze the local order and the dynamical properties corresponding to an atomic hydrogen concentration of ~ 11%, typical of a device quality material. In both crystalline and amorphous cases, our results are in good agreement with available experimental data and give unique insight into the microscopic details of hydrogen incorporation in silicon.
01 Jan 1989
TL;DR: In this paper, the authors present some very recent results on small semiconductor aggregates with special reference to calculations of equilibrium shapes and temperature effects, as well as results of simulations on alkali-metal microclusters.
Abstract: The study of the structural and electronic properties of microclusters is a field of growing interest. Ab-initio molecular dynamics has provided a new and important tool for the theoretical approach to these questions. Here we present some very recent results on small semiconductor aggregates with special reference to calculations of equilibrium shapes and temperature effects. Results of simulations on alkali-metal microclusters are briefly mentioned.
01 Jan 1989
TL;DR: In this article, the properties of both non-crystalline and liquid carbon are investigated, in particular, the structural and electronic properties of the low density disordered phases, the nature of the liquid state and the melting mechanism.
Abstract: The bonded forms of carbon in solid and liquid states have considerable variations with many characteristics which make them interesting for a wide range of researchers1–4. Nevertheless, outstanding questions concerning the properties of both non-crystalline and liquid carbon are yet unanswered; in particular, knowledge of the structural and electronic properties of the low density disordered phases, the nature of the liquid state and the melting mechanism — despite systematic investigations4 of the carbon phase diagram carried out in different fields, such as condensed matter physics1, astrophysics2 and geology3.
TL;DR: The ground state geometries of sulfur clusters S2 to S13 have been calculated using a parameter free density functional (DF) method, combined with molecular dynamics (MD) and simulated annealing techniques as mentioned in this paper.
Abstract: The ground state geometries of sulfur clusters S2 to S13 have been calculated using a parameter‐free density functional (DF) method, combined with molecular dynamics (MD) and simulated annealing techniques. The results are in good agreement with available experimental data, and should provide reliable predictions where detailed measurements are lacking (n=3,4,5,9). The bonding trends are discussed in detail. The MD‐DF approach is particularly valuable in larger clusters, where there are many local energy minima with comparable energies.
01 Jan 1989
TL;DR: In the rapidly growing field of cluster physics, alkali metals have played a key role as discussed by the authors, and the interrelation between stability and structure and electronic properties has been investigated with model calculations which include the effect of realistic electron-ion interactions.
Abstract: In the rapidly growing field of cluster physics alkali metals have played a key role. Due to their relative simplicity of preparation, alkali-metal clusters have in fact been studied experimentally for a longer time and more extensively than aggregates of other materials1,2,3. In particular, abundance spectra have revealed the existence of a regular sequence of “magic numbers” which can be understood with a simple jellium shell model2. The interrelation between stability and structure and electronic properties has been investigated with model calculations which include the effect of realistic electron-ion interactions4 and also with calculations following the standard methods of quantum chemistry5 and solid state theory6.