Inhomogeneity corrections to the Thomas-Fermi-Dirac model of rare-gas diatomic systems

Abstract

Total energies and intermolecular potentials are calculated for the homonuclear diatomic Ne-Ne and Ar-Ar systems according to the Thomas-Fermi-Dirac formulae with a modified Weizsäcker inhomogeneity correction. Using the electron densities of the Hartree-Fock molecular orbital calculations of Gilbert and Wahl as inputs, the inhomogeneity corrections are small compared to the total energies but are comparable to the Dirac exchange contributions at all the available distances. The errors in the total energies using the Thomas-Fermi-Dirac-Weizsäcker formulation are approximately -0·4 per cent for Ne-Ne and -0·01 per cent for Ar-Ar molecules respectively. However, the values of the intermolecular potentials thus calculated are in general too negative and not in agreement with the corresponding Hartree-Fock values. Using instead the electron-gas approximations of Gordon and Kim as inputs, where the superpositions of the atomic Hartree-Fock densities are used, the inhomogeneity contributions are also too negative.