SYMMETRY REDUCTION OF THE MATRIX-ELEMENTS OF A 2-PARTICLE OPERATOR

Local coordinate systems are chosen for each quadruple of atoms relati ve to a four-enter integral, in order to avoid linear combinations of orbitals when symmetry operations perform on an orbital. This choice c an utilize the complete molecular symmetry to attain the optimal numbe r of symmetry-unique integrals and to construct two-particle matrix el ements by multiplying symmetry-unique integrals, called the ''standard four-center integrals,'' by the corresponding coefficients, called th e ''C coefficients.'' A simple algorithm to use the complete molecular symmetry to reduce calculations of molecular matrix elements is outli ned for general highly symmetric molecules. A tetrahedral molecule is analyzed. (C) 1996 John Wiley & Sons, Inc.