Molecular symmetry andab initio calculations. II. Symmetry-matrix and symmetry-supermatrix in the Dirac-Fock method

Abstract

The concepts of symmetry-matrix and symmetry-supermatrix introduced in article I [J. Comput. Chem.,10, 957 (1989)] can be generalized to the Dirac-Fock method. By using the semidirect product decomposition of Oh and the linear vector space theory, the irreducible representation basis of Oh for any molecular system (Oh or its subgroups) can be deduced analytically in the nonorthonormal Cartesian Gaussian basis. This method is extended to discuss the double-valued representations of Oh* in the complex Cartesian Gaussian spinor basis. In the double-valued irreducible representation basis of D2*, the matrix of kinetic operator c(OVERLINE)σ(/OVERLINE)·(OVERLINE)p(/OVELINE) in the Dirac-Fock equation can be reduced into a real symmetric and can be grouped into classes under the operations in D3d. Therefore, the symmetry-matrix and symmetry-supermatrix can also be used in the Dirac-Fock method to reduce the storage of two electron integrals and calculations of Fock matrix during iterations by a factor of ca. g2 (g is the order of the molecular symmetry group). In addition, a method to deal with the nonorthonormal space is presented. © 1996 by John Wiley & Sons, Inc.