ONIOM Method with Charge Transfer Corrections (ONIOM-CT): Analytic Gradients and Benchmarking

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• Hybrid QM/MM methods like ONIOM are crucial for studying large molecular systems.
• Standard ONIOM methods suffer from errors due to link atom treatments, particularly unbalanced charge distribution.
• Previous work introduced ONIOM-CT to correct charge transfer issues using point charges.

Purpose of the Study:

• To derive and implement analytic gradients for ONIOM-CT.
• To generalize ONIOM-CT for systems with multiple link atoms.
• To assess the performance of ONIOM-CT for chemical reactions, including proton transfer.

Main Methods:

• Derivation and implementation of analytic gradients for ONIOM-CT.
• Efficient computation using coupled-perturbed self-consistent equations at a low level of theory.
• Application of ONIOM-CT with Mulliken and Löwdin population analyses for geometry optimizations and reaction energy calculations.

Main Results:

• Analytic gradients for ONIOM-CT were successfully implemented for both single and multiple link atom systems.
• The method was benchmarked on reactions with single link atoms and generalized for multiple link atoms.
• ONIOM-CT demonstrated significant improvements over standard ONIOM for proton transfer reactions.

Conclusions:

• ONIOM-CT with analytic gradients offers an efficient and accurate approach for QM/MM calculations.
• The generalized method expands the applicability of ONIOM-CT to a wider range of complex systems.
• This advancement improves the reliability of computational studies for chemical and biological processes.