Sid Topiol

Valence band and Zn 3d energy levels in Me2Zn from photoelectron spectra and pseudopotential ab initio calculations: electric field gradients in gas phase Zn compounds

Abstract The He I and X-ray photoelectron spectra of the valence levels and Zn 3d levels in Me 2 Zn have been recorded. The orbital ionization potentials are compared with those obtained from our ab initio pseudopotential calculation on Me 2 Zn. There is excellent agreement between predicted and observed values for the outer valence orbitals. The Zn 3d level in Me 2 Zn in split into five peaks due to the combined effect of spin-orbit splitting and crystal field splitting. The major part of the splitting is due to the asymmetric C 0 2 crystal field term which transforms like the electric field gradient. The derived C 0 2 terms for Me 2 Zn and ZnCl 2 are −0.0169 ± 0.0007 eV and −0.011 eV respectively. The observed and calculated splitting confirms an electrostatic (rather than a bonding) origin. The C 0 2 value for Me 2 Zn is consistent with that observed recently for Me 2 Cd.

The use of pseudopotentials within local-density formalism calculations for atoms: Some results for the first row

Abstract The use of a pseudopotential to replace the core electron density within electronic structure calculations of Kohn-Sham type is proposed. An heuristic derivation of such a potential is given. Within the local exchange-correlation scheme, the pseudopotential employed is precisely equivalent to solving a frozen-core problem; this is quite different from the situation encountered in using pseudopotentials in Hartree-Fock calculations, where additional approximations are involved. Numerical results for several excited and ionic states of first row atoms are given: the errors due to the frozen core are less than 10 −3 hartree.

Ab-initio calculation, using ab-initio pseudopotentials, of some electronic properties of ethane, methylsilane and disilane

Abstract Recently-developed ab-initio pseudopotentials are employed for the calculation of electronic energy levels and internal rotation barriers in C 2 H 6 , CH 3 SiH 3 and Si 2 H 6 . The calculations are performed at the experimental internal geometry, using double-zeta quality gaussian basis sets. The results show that the errors caused by the use of the pseudo-potential are negligible compared to those of limited basis-set size, so that the pseudopotentials can indeed be used to replace the core electrons.

On the use of minimal valence basis sets with the coreless Hartree–Fock effective potential

We investigate the reliability of calculated properties obtained by the coreless Hartree–Fock effective potential method with minimal valence basis sets. Three different types of minimal valence basis sets are constructed and tested. Optimized bond lengths are typically too long, while bond angles are similar to those obtained from all electron calculations. Properties closely related to the electronic charge distribution, such as dipole moments and orbital energies, are quite satisfactory when calculated at fixed geometries.

Use of pseudopotentials within the floating spherical Gaussian orbital method: Calculations on methane

The utility of nonempirical pseudopotentials in floating spherical Gaussian orbital (FSGO) calculations is examined. Calculations on the methane molecule with various popular pseudopotentials reveal that the best pseudopotentials may not be the most compatible with FSGO’s, but that in all cases, proper treatment of the angular momentum dependence is important.

Angular momentum dependence of pseudopotentials: calculation of the potential curve for HF

Abstract The question of angular momentum dependence of pseudopotentials or use in molecular electronic structure calculations is investigated. It is found that for the HF molecule it is sufficient to cut off the pseudopotential on the F atom at l = 1 (lmax = lcore + 1).

Pseudopotential calculations: some electronic properties of zinc dichloride

Abstract Ab-initio calculations are performed for the ZnCl 2 molecules, employing recently-developed pseudopotential methods. Two separate calculations are discussed, one treating the d-electrons explicitly, the other including the ds in the core. The description of the valence region seems satisfactory, with only negligible errors arising from the use of the pseudopotential. Comparison is made to the photoelectron spectrum, and to the ZnF 2 molecule.

Ab-initio electronic structure studies of mobility paths in fast-ion conductors—I: Results for MI4−3 clusters

Abstract We report results of minimum-basis Pseudopotential Hartree-Fock studies of MI 4 −3 clusters ( M = Na + , K + , Ag + , and Cu + ), and of HgI 4 −2 . The calculations are designed to characterize local-site effects on mobility paths in solid state electrolytes. We observe qualitatively correct behavior, with Ag + predicted to be the most mobile ion. Quadrupolar polarizability of the metal ion, which is produced by s - d mixing, lowers the energy of trigonal transition state, thus accounting for the observation that quadrupole polarizable species are ideal mobile ions in close-packed halide frameworks. Mulliken populations show that there is considerable local covalency, so that electrostatic potential studies must be done very carefully. Expansion of the I 4 tetrahedron lowers the barrier energy.

Ab initio Studies, using the FSGO-pseudopotential method, of the electronic structure in group IV cluster molecules M(LH3)4; M, L = C, Si, Ge

Ab initio FSGO-pseudopotential studies are reported for the nine molecules M(LH3)4; M, L = C, Si, Ge. We report orbital energies, calculated geometries, bonding parameters, and predicted energies of reaction. Comparison with experimental data shows the results to be quite satisfactory. Comparison with the tetrahedral group IV solids affords some clues to the nature of the doped materials. The outstanding observation, from all parameters calculated, is the similarity of (Si, Ge) and their difference from carbon. Comments on possible stability of the compounds are ventured.

First-principles pseudopotential in the local-density-functional formalism

Abstract A first principles approach to the pseudopotential method is developed in the local density formalism (LDF). As an example, tests on the carbon and tungsten atom potentials are given. Comparison of the energy eigenvalues and total energy differences obtained in accurate self-consistent numerical solutions of the all-electron problem with those of the pseudopotential problem reveals an error smaller than 10 −3 au for a very wide range of electronic configuration and excitation states. Charge density observables such as moments of r and X-ray scattering factors are also accurately obtained. Apllications to large-scale electronic structure calculations as well as comparison of the results with the empirical pseudopotential scheme are discussed.