Pseudospectral localized Mo/ller–Plesset methods: Theory and calculation of conformational energies

We have developed an algorithm based upon pseudospectral ab initio electronic structure methods for evaluating correlation energies via the localized Mo/ller–Plesset methodology of Pulay and Saebo. Even for small molecules (∼20 atoms) CPU times are diminished by a factor of ∼10 compared to canonical MP2 timings for Gaussian 92 and the scaling is reduced from N4−N5 in conventional methods to ∼N3. We have tested the accuracy of the method by calculating conformational energy differences for 36 small molecules for which experimental 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 0.18 kcal/mol between theory and experiment is obtained, with a maximum deviation of ∼0.55 kcal/mol. This performance is significantly better than that obtained previously with a smaller basis set via canonical MP2; it is also superior to the results of gradient corrected density func...