On the use of symmetry in first-order perturbed Hartree-Fock theory

A method for the determination of the symmetry of first-order vectors in Hartree-Fock perturbation theory is developed. This leads to the definition of symmetry-adapted basis vectors to be employed at first order in the perturbation. It is shown that computer time can be saved, to some extent, in the calculation of second-order properties, by exploiting molecular symmetry. Specific examples are given for methane, ammonia, and water