Quasi-classical Molecular Dynamics Simulations of the Electron Gas: Dynamic properties

Results of quasi-classical molecular dynamics simulations of the quantum electron gas are reported. Quantum effects corresponding to the Pauli and the Heisenberg principle are modeled by an effective momentum-dependent Hamiltonian. The velocity autocorrelation functions and the dynamic structure factors have been computed. A comparison with theoretical predictions was performed.Comment: 8 figure

Optimization of inhomogeneous electron correlation factors in periodic solids

A method is presented for the optimization of one-body and inhomogeneous two-body terms in correlated electronic wave functions of Jastrow-Slater type. The most general form of inhomogeneous correlation term which is compatible with crystal symmetry is used and the energy is minimized with respect to all parameters using a rapidly convergent iterative approach, based on Monte Carlo sampling of the energy and fitting energy fluctuations. The energy minimization is performed exactly within statistical sampling error for the energy derivatives and the resulting one- and two-body terms of the wave function are found to be well-determined. The largest calculations performed require the optimization of over 3000 parameters. The inhomogeneous two-electron correlation terms are calculated for diamond and rhombohedral graphite. The optimal terms in diamond are found to be approximately homogeneous and isotropic over all ranges of electron separation, but exhibit some inhomogeneity at short- and intermediate-range, whereas those in graphite are found to be homogeneous at short-range, but inhomogeneous and anisotropic at intermediate- and long-range electron separation.Comment: 23 pages, 15 figures, 1 table, REVTeX4, submitted to PR

Selective correlation scheme within diffusion quantum Monte Carlo

We present a selective correlation scheme allowing us to correlate only subsets of electrons, which can be assigned to arbitrary groups of orbitals, within diffusion quantum Monte Carlo calculations. The set of occupied orbitals, obtained from an all-electron mean-field calculation, is divided into two parts: frozen orbitals and explicitly considered orbitals. Electrons residing in frozen orbitals are excluded from the correlation treatment and handled within mean-field theory. The effects of such electrons on the remaining correlated electrons are represented by a model potential consisting of Coulomb and exchange parts, combined with a projectionlike operator to ensure orthogonality between the two sets of orbitals. Applying a localization procedure, similar to that used in connection with atomic semilocal pseudopotentials, to the exchange and projectionlike operators, local many-particle representations of these operators are obtained, which are suitable for use within quantum Monte Carlo calculations. While localizing the exchange part is rather straightforward, special care has to be taken to localize the projectionlike operator properly. As an illustrating example we consider the nitrogen dimer with the triple bond being correlated, while the nonbonding orbitals are kept frozen. By comparison with coupled cluster calculations, we demonstrate that with properly localized operators, the correlation energy of the triple bond can be quantitatively recovered. ©2002 American Institute of Physics