Monte Carlo free energy calculations using electronic structure methods

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Chemical Dynamics

Background:

• Traditional molecular mechanics-based importance sampling (MMBIF) requires system-specific force fields.
• Simulating reactive chemical systems often necessitates advanced sampling techniques.

Purpose of the Study:

• To extend the MMBIF algorithm by incorporating semiempirical electronic structure methods.
• To develop a fully quantum mechanical Monte Carlo sampling method for reactive systems.
• To enable simulations without the need for system-specific force fields.

Main Methods:

• Integration of semiempirical electronic structure methods into the secondary Markov chain of MMBIF.
• Application of thermodynamic integration to calculate the potential of mean force for HCN isomerization.
• Implementation of constraints using a modified SHAKE algorithm, including a fixed reaction coordinate.

Main Results:

• The new method achieves sampling efficiency comparable to traditional MMBIF with system-specific force fields.
• The semiempirical approach provides a viable alternative for systems lacking suitable molecular mechanics force fields.
• Successful application to calculating the potential of mean force for HCN isomerization.

Conclusions:

• The developed quantum mechanical Monte Carlo method is a powerful tool for simulating reactive chemical systems.
• This approach broadens the applicability of importance sampling to systems where MM force fields are not feasible.
• It offers a flexible and efficient alternative for computational chemistry research.