Hybrid RHF/MP2 geometry optimizations with the Effective Fragment Molecular Orbital Method

TL;DR

This paper extends the effective fragment molecular orbital method to include MP2 level treatment of a single fragment, improving accuracy and convergence in geometry optimizations for enzymatic reactions.

Contribution

It introduces a hybrid RHF/MP2 approach within the effective fragment molecular orbital framework for more accurate geometry optimizations.

Findings

MP2 optimizations lower reaction barriers by up to 3.5 kcal/mol.

The method improves convergence with respect to basis set size.

CPU time roughly doubles compared to RHF for double zeta basis sets.

Abstract

The frozen domain effective fragment molecular orbital method is extended to allow for the treatment of a single fragment at the MP2 level of theory. The approach is applied to the conversion of chorismate to prephenate by chorismate mutase, where the substrate is treated at the MP2 level of theory while the rest of the system is treated at the RHF level. MP2 geometry optimization is found to lower the barrier by up to 3.5 kcal/mol compared to RHF optimzations and ONIOM energy refinement and leads to a smoother convergence with respect to the basis set for the reaction profile. For double zeta basis sets the increase in CPU time relative to RHF is roughly a factor of two.