Stress tensor and constant pressure simulation for polarizable Gaussian multipole model

Area of Science:

• Computational Chemistry
• Molecular Dynamics Simulations
• Physical Chemistry

Background:

• Previous work established the theory for molecular dynamics (MD) simulations using polarizable Gaussian multipole (pGM) electrostatics.
• The covalent basis vector framework and closed-form energy/force expressions were developed for efficient pGM implementation.

Purpose of the Study:

• To derive the pGM internal stress tensor for constant pressure MD simulations.
• To present formulations for flexible, rigid, and short-range screened systems.
• To validate the implementation and assess simulation behavior compared to point charge models.

Main Methods:

• Derivation of analytical formulations for the pGM internal stress tensor.
• Implementation within the SANDER program of the Amber package.
• Validation using finite-difference methods and constant temperature/pressure MD simulations of pGM water molecules.

Main Results:

• Successful derivation and implementation of the pGM internal stress tensor.
• MD simulations of pGM water molecules stabilized at physically reasonable states, balancing external pressure.
• Observed fundamental differences in simulation behavior between pGM and classic point charge models.

Conclusions:

• The derived pGM internal stress tensor enables stable constant pressure MD simulations.
• The pGM model exhibits distinct behaviors compared to point charge models, highlighting the need for further parameterization.
• This work advances the application of pGM electrostatics in molecular simulations.