A New Direct Minimization Algorism for Hartree-Fock Calculation

Abstract

A new density matrix algorism is proposed for the Hartree-Fock calculation in the restricted basis approximation. The algorism is shown to have a satisfactory behavior in convergence. It is also capable of obtaining high energy solutions of the Hartree-Fock equation. A CNDO/2 computer program for the closed shell case making use of the new algorism is tested mainly for carbon mono-oxide. Its computational speed is comparable to that of the usual method at the equilibrium nuclear configuration. It becomes faster than the usual one as the interatomic distance increases and converges with a nearly constant speed even at nuclear configurations where the usual one does not converge. The structure of the Hartree-Fock energy sufrace in the variation space is illustrated for the carbon mono-oxide with various interatomic distances. The origin of the troubles in convergence is discussed in connection with the structure of the surface. The Hartree-Fock solutions corresponding to the extrema of the surface are calculated and some of them are shown to represent the zwitter ionic states of the molecule.