Self-consistent, nonorthogonal group function approximation for polyatomic systems. I. Closed shells

Abstract

The wavefunction of a closed shell system in the orbital product approximation is reformulated into a product of nonorthogonal group functions, and a variational method based on local energy functionals is developed for the determination of the orbital equations. The orbitals are expanded in terms of local bases, and a double iterative procedure based on Roothaan’s method is used to compute the self-consistent solutions of the equations. The use of local energy functionals and nonothogonal groups permits the replacement of the usual system of equations by several systems of lower dimensionality. In addition, the number of electron interaction integrals required for the solution of the orbital equations is reduced, leading to a simplification in the calculation of the required matrix elements. This method is applied to hydrogen fluoride and lithium hydroxide, and calculations from a number of wavefunctions with differing group function structure are compared with the Hartree–Fock results.