Analytical energy gradients for local second-order Møller-Plesset perturbation theory using intrinsic bond orbitals

Abstract

ABSTRACTWe present the theory and an implementation for PAO-LMP2 analytical energy gradients (local second-order Møller-Plesset perturbation theory with domains of projected atomic orbitals), using intrinsic bond orbitals (IBOs). The accuracy of optimised LMP2 geometry parameters relative to canonical MP2 and CCSD(T) ones is benchmarked for more than 100 small- to medium-sized molecules. Using augmented triple-ζ basis sets, the deviations of computed LMP2 bond lengths and bond angles from the corresponding MP2 ones are small and quickly decrease with increasing domain sizes. For small domains, a systematic compensation between the intrinsic error of MP2 and the errors due to the local approximations is found, so that the LMP2 results deviate less from CCSD(T) than the MP2 ones. On the other hand, with extended domains, the differences between LMP2 and MP2 geometry parameters become negligible.