Showing papers by "David Vanderbilt published in 1986"

Molecular dynamics and ab initio total energy calculations

Abstract: In a recent Letter, ' Car and Parrinello described a molecular-dynamics approach to total-energy calculations that allows global minimization of the total energy to be achieved with respect to both electronic and ionic coordinates. In this Comment, we shall briefly describe a number of modifications we have made to Car and Parrinello s method that can significantly increase the speed of the computation. Car and Parrinello write the equation of motion (EOM) for the electronic state $„„as

Dissipation due to a "valley wave" channel in the quantum Hall effect of a multivalley semiconductor.

Abstract: When the quantized Hall effect occurs at a semiconductor surface such as Si(110), where the carriers have a time-reversal valley degeneracy, there should be a spontaneous valley polarization at appropriate values of the filling factor ..nu... There can then be dissipation at T-italic = 0 due to radiation of Goldstone bosons (''valley waves'') at impurity sites, provided that the current density exceeds a critical value j-italic/sub c-italic/ determined by the intervalley electron-electron scattering or other terms which modify the valley-wave dispersion at long wavelengths. The dissipation above j-italic/sub c-italic/ is described by a constant resistivity rho/sub x-italic//sub x-italic/, which should be small but measureable, and sensitive to the density of neutral impurities.

Calculation of anharmonic phonon couplings in C, Si, and Ge

Abstract: Frozen-phonon total-energy calculations are used to extract anharmonic phonon couplings for the tetrahedral elements C, Si, and Ge. The local-density approximation is employed, with a localized-orbital basis used for C and a plane-wave expansion used for Si and Ge. The bare interactions between optical phonons are completely determined through fourth order at the Brillouin-zone center. These are used to compute renormalized couplings, in which a vertex is screened by virtual phonons. The renormalized couplings are found to have the wrong sign to allow formation of a proposed two-phonon bound state in diamond.

Application of a general self-consistency scheme in the linear combination of atomic orbitals formalism to the electronic and structural properties of Si and W

Abstract: %'e present a general self-consistency procedure formulated in momentum space for electronic structure and total-energy calculations of crystalline solids. It is shown that both the charge density and the change in the Hamiltonian matrix elements in each iteration can be calculated in a straightforward fashion once a set of overlap matrices is computed. The present formulation has the merit of bringing the self-consistency problem for different basis sets to the same footing. The scheme is used to extend a first-principles pseudopotential linear combination of Gaussian orbitals method to full point-by-point self-consistency, without refitting of potentials. It is shown that the set of overlap matrices can be calculated very efficiently if we exploit the translational and space-group symmetries of the system under consideration. This scheme has been applied to study the structural and electronic properties of Si and %, prototypical systems of very different bonding properties. The results agree well with experiment and other calculations. The fully self-consistent results are compared with those obtained by a variational procedure [J. R. Chehkowsky and S. G. Louie, Phys. Rev. 8 29, 3470 (1984)). We find that the structural properties for bulk Si and W (both systems have no interatomic charge transfer) can be treated accurately by the variational procedure. However, full self-consistency is needed for an accurate description of the band. energies.

Theoretical study of the cohesive and structural properties of Mo and W in bcc, fcc, and hcp structures

Abstract: The structural properties of Mo and W in the bcc, fcc, and hcp structures are calculated using a fully-self-consistent pseudopotential linear combination of atomic orbitals method. Equilibrium lattice constants, cohesive energies, bulk moduli, differences in structural energies, and Mulliken-population analyses are obtained. For both elements, the bcc structure is found to be the most stable while the fcc and hcp structures have very similar cohesive energies. We find that the difference in the sum of eigenvalues gives the correct sign but not the magnitude for the difference in total energy between the bcc and fcc structures.