Numerical Hartree-Fock and correlation calculations for molecules

Numerical Hartree-Fock and perturbation calculations that have been performed on molecules are reviewed and the importance of using multidimensional reference functions is emphasized. Atomic, multireference calculations are then discussed and numerical results are given for the ground state of the neutral beryllium atom. Our approach is to perform a MCHF calculation for the strongly interacting configurations and then to use perturbation theory systematically to improve upon the accuracy of this description. The effect of excitations from the MCHF states are calculated by solving inhomogeneous one- and two-particle equations for the particular linear combinations of excited states which contribute. Then numerical calculations are reported on the elementary molecular ion, H32+, using a spline function technique, and the prospect of using this approach for larger molecules and for clusters of metal atoms is discussed. This last work is being carried out in collaboration with C. Bottcher and G. Bottrel of the Oak Ridge National Laboratory. (orig.)