Relativistic Corrections to the Electron Density at the Nuclear Surface and to the Alkali Halide Overlap Integrals

The electron density at the nuclear surface and the alkali halide overlap integrals have been calculated with Hartree—Fock, Hartree—Fock—Slater, and the relativistic Dirac—Slater SCF wavefunctions. Both the full Slater exchange and ⅔ of it have been used.The SCF relativistic enhancements of the electronic density at the nuclear surface are in good agreement with the enhancements predicted by Racah and by Rosenthal and Breit. The Slater exchange approximation slightly overestimates the density at small radii for valence electrons, but gives excellent results for core electrons.The alkali halide overlap integrals are extremely dependent on the amount of Slater exchange used, thus implying that this approximation is less satisfactory for large radii. Our results indicate that the multiplicative factor modifying the Slater exchange should be between ⅔ and 1 for the calculation of overlap integrals. The overlap integrals for the heavier alkali halides are reduced by about 10% by relativistic effects.