A study of localized molecular orbitais by the group theory method and its approach to the many-electron correlation problem: Part 2. The point group symmetry and calculation program of spin-free Hamiltonian matrix elements

Abstract

The use of group symmetric localized molecular orbitals as configuration generating orbitals of many-electron valence bond functions, namely bonded tableaux (BTs ), greatly simplifies the calculation of the Hamiltonian matrix elements. A practical algorithm and program for such calculations was developed, which includes the calculation of the overlap integral between the BTs and the action of the generators and of the generator products of the unitary group on the BT states, and the Hamiltonian matrix elements are expressed in terms of a linear combination of nonequivalent two-centre and four-centre integrals and geometric factors based on the Wigner-Eikart law.