Efficient Calculation of Free Energy Differences Associated with Isotopic Substitution Using Path-Integral Molecular...

Area of Science:

• Quantum Chemistry
• Computational Physics
• Chemical Thermodynamics

Background:

• Isotopic substitution alters chemical system equilibrium properties.
• These shifts are quantum mechanical effects.
• The Feynman path integral approach quantifies these effects.

Purpose of the Study:

• Develop a highly efficient path integral scheme for computing free energy differences.
• Improve computational efficiency in quantum mechanical calculations.

Main Methods:

• Employing a mass switching function based on inverse square root of mass.
• Utilizing a single-point thermodynamic integration approach.
• Deriving fourth-order free energy derivative estimators based on Takahashi-Imada scheme.

Main Results:

• The mass switching function ensures a constant free energy derivative in the harmonic limit.
• A novel fourth-order virial estimator reduces numerical noise and computational demands.
• The new estimator converges smoothly with fewer imaginary time points.

Conclusions:

• The developed path integral scheme significantly enhances computational efficiency.
• Accurate free energy differences due to isotopic substitution can be computed more effectively.
• This methodology offers a powerful tool for studying quantum mechanical effects in chemical systems.