Comparative study of the Hartree–Fock and the Hartree–Fock–Slater method

Abstract

AbstractThe Hartree–Fock method (standard Roothaan closed‐shell HF–LCAO theory) and the Hartree–Fock–Slater method (restricted HFS–LCAO–DV method developed by Baerends and Ros) have been compared with emphasis on the respective one‐electron equations and on the matrix elements of the respective Fock operators. Using the same STO basis in the two cases, the matrix elements of the Fock operators and of their separate one‐electron, Coulomb, and exchange contributions have been calculated for the same orbitals and density of the ground state of the diatomic molecule ZnO. The effects of methodical (exchange potential) and numerical (DV method, density fit) differences between the HF and HFS methods on the various matrix elements have been analyzed. As expected the methodical effect prevails and is responsible for the higher (less negative) values of the matrix elements of the HFS Fock operator compared to those of the HF Fock operator. Numerical effects are observable also and are caused by the difference in integration procedures (DV method), not by the density fit.