Combining Quantum Mechanics Methods with Molecular Mechanics Methods in ONIOM

Area of Science:

• Computational Chemistry
• Quantum Mechanics/Molecular Mechanics (QM/MM)

Background:

• The ONIOM(QM:MM) method combines quantum mechanics (QM) and molecular mechanics (MM) for large system calculations.
• Standard ONIOM includes electrostatic interactions at a classical level.
• Link atom corrections are implicit in ONIOM but not in standard QM/MM.

Purpose of the Study:

• To present extensions to the ONIOM(QM:MM) scheme, specifically electronic embedding.
• To compare the stability of ONIOM with electronic embedding against QM/MM with electronic embedding.
• To demonstrate practical aspects and potential limitations of ONIOM(QM:MM) calculations.

Main Methods:

• Implementation and testing of ONIOM with electronic embedding.
• Comparative analysis of ONIOM and QM/MM methods with electronic embedding.
• Investigation of potential surface behavior during bond-breaking/forming events in ONIOM.

Main Results:

• ONIOM with electronic embedding demonstrates enhanced stability compared to QM/MM with electronic embedding.
• The link atom correction in ONIOM is analyzed.
• Discontinuities in the potential surface are observed in ONIOM(QM:MM) when bond breaking/forming occurs near the MM region.

Conclusions:

• Electronic embedding offers a more stable approach for ONIOM(QM:MM) calculations.
• Care must be taken regarding potential surface discontinuities in ONIOM when simulating reactions near the QM/MM boundary.