Combining Quantum Mechanics Methods with Molecular Mechanics Methods in ONIOM

TLDR

In its original formulation, ONIOM(QM:MM) includes electrostatic interactions between regions at the classical level. The authors aim to extend ONIOM(QM:MM) by adding electronic embedding and link‑atom corrections, and to demonstrate practical aspects of the method. They implement these extensions by incorporating electronic embedding and link‑atom corrections into the ONIOM framework and illustrate the approach with practical calculations. The extended ONIOM with electronic embedding proves more stable than QM/MM with electronic embedding, yet the potential surface can become discontinuous when bond breaking or forming occurs within three bonds of the MM region.

Abstract

The purpose of this paper is 2-fold. First, we present several extensions to the ONIOM(QM:MM) scheme. In its original formulation, the electrostatic interaction between the regions is included at the classical level. Here we present the extension to electronic embedding. We show how the behavior of ONIOM with electronic embedding can be more stable than QM/MM with electronic embedding. We also investigate the link atom correction, which is implicit in ONIOM but not in QM/MM. Second, we demonstrate some of the practical aspects of ONIOM(QM:MM) calculations. Specifically, we show that the potential surface can be discontinuous when there is bond breaking and forming closer than three bonds from the MM region.