Efficient calculation of canonical MP2 energies

An efficient canonical second-order Moller-Plesset theory (MP2) procedure, based on the Saebo-Almlof integral - direct transformation technique, coupl ed with efficient prescreening of the atomic orbital (AO) integrals, is des cribed. For large molecules, a fraction of the AO integrals suffices to pro duce energies to microhartree accuracy. Calculations up to 1800 basis funct ions and 240 correlated electrons have been performed on a single processor computer for symmetrical molecules. Calculations with similar to 1000 basi s functions and similar to 120 electrons can be performed routinely for mol ecules with no symmetry. However, scaling of the second half transformation is still steep. Several basis sets used in correlated calculations are com pared for economy and performance. (C) 2001 Elsevier Science B.V. All right s reserved.