Optimization of Alchemical Pathways Using Extended Thermodynamic Integration.

Area of Science:

• Computational chemistry
• Molecular simulation
• Physical chemistry

Background:

• Thermodynamic integration (TI) is a standard method for calculating free-energy differences.
• A key challenge in TI is the need for extensive sampling of intermediate states (λ-states) to accurately integrate ⟨∂H/∂λ⟩.
• This often leads to inefficient simulations and potential inaccuracies.

Purpose of the Study:

• To investigate the utility of extended thermodynamic integration (TI) for optimizing Hamiltonian parameterization (H(λ)).
• To assess the impact of different parameterizations on the smoothness of ⟨∂H/∂λ⟩ curves and overall simulation efficiency.
• To identify optimal parameterization strategies for specific applications like hydration and binding free energy calculations.

Main Methods:

• Utilized the extended thermodynamic integration (TI) approach.
• Explored various parameterizations of the Hamiltonian (H(λ)).
• Analyzed the curvature of ⟨∂H/∂λ⟩ curves and simulation efficiency.

Main Results:

• Extended TI effectively identifies parameterizations that result in low-curvature ⟨∂H/∂λ⟩ profiles.
• An optimal parameterization strategy was proposed for calculating hydration free energies.
• Optimized Hamiltonian parameterizations in the unbound state were shown to reduce curvature in the bound state for relative binding free energy calculations.

Conclusions:

• Extended TI offers a powerful tool for selecting efficient and accurate Hamiltonian parameterizations in free-energy calculations.
• The proposed methods can significantly improve the computational efficiency and reliability of molecular simulations.
• This work provides practical guidelines for optimizing TI simulations in computational chemistry.