PSEUDOSPECTRAL LOCALIZED MOLLER-PLESSET METHODS - THEORY AND CALCULATION OF CONFORMATIONAL ENERGIES

We have developed an algorithm based upon pseudospectral ab initio ele ctronic structure methods for evaluating correlation energies via the localized Moller-Plesset methodology of Pulay and Saebo. Even for smal l molecules (similar to 20 atoms) CPU times are diminished by a factor of similar to 10 compared to canonical MP2 timings for Gaussian 92 an d the scaling is reduced from N-4-N-5 in conventional methods to simil ar to N-3. We have tested the accuracy of the method by calculating co nformational energy differences for 36 small molecules for which exper imental data exists, using the Dunning cc-pVTZ correlation consistent basis set. After removing 6 test cases on the grounds of unreliability of the experimental data, an average deviation with experiment of 0.1 8 kcal/mol between theory and experiment is obtained, with a maximum d eviation of similar to 0.55 kcal/mol. This performance is significantl y better than that obtained previously with a smaller basis set via ca nonical MP2; it is also superior to the results of gradient corrected density functional theory. (C) 1995 American Institute of Physics.