Ionic Soft Sphere Parameters from Hartree-Fock-Slater Calculations

The soft sphere parameters for many closed shell ions from He through U6+, as well as many ions of the 3d, 4d, 5d, and 4f transition series were computed from charge densities obtained from Hartree-Fock-Slater calculations. For each ion, a radius R0 at which the charge density ρc is exp (−4.3) a.u., and a softness ρ which appears in ln(ρc)=−4.3+(R0−r)/ρ were obtained. These characterize the charge density in the outer region of the ion, that is, on the order of 0.5 electrons lie outside a sphere of radius R0. In addition, an electron affinity A was computed for each ion, being taken as the ionization potential for the ion with one added electron. Use of these parameters in semiempirical theories of ionic crystals, such as the Born-Mayer theory of hard core repulsive forces, and the soft sphere model of electric field gradients at nuclei, is briefly discussed.