MULTIREFERENCE MOLLER-PLESSET PERTURBATION-THEORY FOR HIGH-SPIN OPEN-SHELL SYSTEMS

New forms of multireference Moller-Plesset perturbation theory are presented that are applicable to high-spin open-shell systems. The second-order perturbation theory based on the multireference function yields large parts of dynamical correlation corrections for a relatively low computational cost. Results are reported for the energy difference between the 1A1 and 3B1 states of CH2 and for the potential energy curve of the triplet ground state (3-SIGMA(g)-) of O2. In spite of the drastic simplification, results are encouraging.