Hartree–Fock diamond results illustrating two integral approximations

Abstract

Two different procedures for approximating the smaller two-electron integrals in ab-initio molecular and crystalline Hartree–Fock calculations are discussed and illustrated on diamond. One approximation is due to H. Kashiwagi. The other uses two alternate expressions for the first-order density matrix. The usual expression in terms of the wavefunction basis is used for the integrals involving basis function products with a large pseudocharge. A more approximate expression in terms of the total charge associated with each atom–atom pair is used for integrals involving the smaller basis function products. Crystalline Hartree–Fock diamond results are given to allow comparison of total energies, one-electron eigenvalues, x-ray structure factors, and directional Compton profiles.