Understanding cross-boundary events in ONIOM QM:QM %26apos; calculations

作者：Lundberg Marcus^*

来源：Journal of Computational Chemistry, 2012, 33(4): 406-415.

DOI：10.1002/jcc.21982

• multiscale modeling
• reactivity
• serine protease
• hydrogen bonds
• QM simulations

QM:QM%26apos; models, where QM%26apos; is a fast molecular orbital method, offers advantages over standard quantum mechanics: molecular mechanics (QM:MM) models, especially in the description of charge transfer and mutual polarization between layers. The ONIOM QM:QM%26apos; scheme also allows for reactions across the layer boundary, but the understanding of these events is limited. To explain the factors that affect cross-boundary events, a set of proton transfer processes, including the acylation reaction in serine protease, have been investigated. For reactions inside out, that is, when a group breaks a bond in the high layer and forms a new bond with a group in the low layer, QM%26apos; methods that are overbinding relative to the QM method, for example, Hartree-Fock versus B3LYP, can severely overestimate the exothermicity of the reaction. This might lead to artificial reactivity across the QM:QM%26apos; boundary, a phenomenon called model escape. The accuracy for reactions that occur outside in, that is, when a group in the low layer forms a new bond with the high layer, is mainly determined by the QM%26apos; calculation. Cross-boundary reactions should generally be avoided in the present ONIOM scheme. Fortunately, a better understanding of these events makes it easy to design stable ONIOM QM:QM%26apos; models, for example, by choosing a proper model system. Importantly, an accurate description of cross-boundary reactions would open up possibilities to simulate chemical reactions without a priori limiting the reactivity in the design of the computational model. Challenges to implement a simulation scheme (ONIOM-XR) that can automatically handle chemical reactions between different layers are briefly discussed.

• 出版日期2012-2-5