Applying efficient implicit nongeometric constraints in alchemical free energy simulations

Area of Science:

• Computational Chemistry
• Molecular Dynamics Simulations

Background:

• Molecular dynamics simulations require geometric constraints.
• Alchemical free energy perturbation simulations necessitate nongeometric constraints.
• Existing methods for handling constraints in simulations are limited.

Purpose of the Study:

• To develop novel functional forms for multisite λ-dynamics simulations.
• To implicitly satisfy nongeometric constraints in alchemical transformations.
• To improve sampling and convergence rates in molecular dynamics.

Main Methods:

• Developed four new functional forms for λ parameters in multisite λ-dynamics.
• Constrained λ parameters such that 0 ≤ λ(i) ≤ 1 and Σ λ(i) = 1.
• Utilized model systems to test functional forms and assess simulation stability with a 2 fs timestep.

Main Results:

• All four functional forms yielded stable simulations.
• The functional form λ(i) = e(c sinθ(i))/Σ e(c sinθ(j)) demonstrated enhanced sampling profiles.
• This specific functional form showed improved convergence rates compared to other tested forms.
• The chosen functional form oscillates between 0 and 1 with steep transitions.

Conclusions:

• The presented functional forms effectively satisfy nongeometric constraints in molecular dynamics.
• The specific exponential sine function offers superior sampling and faster convergence for alchemical free energy simulations.
• This method provides a stable and efficient approach for complex molecular simulations.