Tracing the minimum-energy path on the free-energy surface

Area of Science:

• Chemical Physics
• Computational Chemistry
• Molecular Dynamics

Background:

• Estimating reaction free-energy profiles is crucial in chemistry.
• Molecular dynamics simulations with constraints are common but temperature effects on reaction paths are significant.
• Existing methods may not accurately capture finite-temperature reaction dynamics.

Purpose of the Study:

• To develop a practical method for constructing the minimum free-energy path (MFEP) on the free-energy surface at a given temperature.
• To provide a computationally efficient approach for analyzing reaction mechanisms under realistic conditions.
• To compare temperature-dependent reaction paths with zero-Kelvin approximations.

Main Methods:

• Utilizing the blue-moon ensemble method to derive free-energy gradients along a reaction coordinate (RC).
• Employing these gradients to locate the MFEP on the free-energy surface, analogous to Fukui's intrinsic reaction path.
• Calculating the free-energy profile via thermodynamic integration once the MFEP is determined.
• Investigating the cancellation of mass-metric corrections for simplified calculations.

Main Results:

• A practical method for determining the minimum free-energy path at finite temperatures was successfully developed.
• The study demonstrated that mass-metric corrections often cancel, simplifying the computational procedure.
• The minimum free-energy path for CCl2 addition to ethylene at 300 K was computed and compared to a 0 K path and a simple 1D RC path.

Conclusions:

• The proposed method offers a reliable way to find temperature-dependent minimum energy reaction paths.
• This approach enhances the accuracy of molecular dynamics simulations for chemical reactions.
• The findings facilitate a better understanding of reaction mechanisms influenced by thermal effects.