Energy density analysis for second-order Moller-Plesset perturbation theory and coupled-cluster theory with singles and doubles:: Application to C2H4-CH4 complexes

Grid-based energy density analysis (EDA), in which numerical integration is performed for two-electron integrals by the pseudospectral method (Imamura et al., J. Chem. Phys. 2007, 126, 034103), is extended to correlated methods: second-order Moller-Plesset (MP2) perturbation and coupled-cluster singles and doubles (CCSD). Using EDA for MP2 and CCSD, we estimate atomic correlation energy differences and con-elation energy density difference maps for C2H4-CH4 complexes. The analyses confirm that polarization and diffuse functions essentially contribute to the descriptions of weak interaction around the nuclei and in the area between C2H4 and CH4, respectively. (C) 2008 Wiley Periodicals, Inc.