Application of resolution of identity approximation of second-order Moller-Plesset perturbation theory to three-body fragment molecular orbital method

The resolution of identity (RI) approximation of second-order Moller-Plesset perturbation (MP2) theory, termed as RI-MP2, is applied to three-body fragment molecular orbital (FMO3) method. New implementation of FMO3 RI-MP2 is developed based on an efficient parallel RI-MP2 code developed recently in our group. Using this new implementation, the accuracy and computational time of FMO3 RI-MP2 calculations are assessed for water clusters, polyalanines, and proteins. The errors arising from RI-MP2 are sufficiently small in the FMO3 MP2 calculations that they give quantitative accuracy for practical chemical applications. Considerable time savings are attained in the FMO3 MP2 calculations with the application of RI-MP2.