Explicit Symplectic Integrators of Molecular Dynamics Algorithms for Rigid-Body Molecules in the Canonical, Isothermal-Isobaric, and Related Ensembles

TL;DR

This paper introduces explicit symplectic integrators for molecular dynamics simulations of rigid-body molecules across various ensembles, demonstrating improved stability and Hamiltonian conservation over traditional methods.

Contribution

The authors develop new explicit symplectic integrators tailored for rigid-body molecular dynamics in multiple ensembles, enhancing stability and energy conservation.

Findings

Symplectic integrators conserve Hamiltonian more accurately.

Longer time steps (up to 4 fs) are feasible with symplectic methods.

Enhanced stability compared to nonsymplectic algorithms.

Abstract

We propose explicit symplectic integrators of molecular dynamics (MD) algorithms for rigid-body molecules in the canonical and isothermal-isobaric ensembles. We also present a symplectic algorithm in the constant normal pressure and lateral surface area ensemble and that combined with the Parrinello-Rahman algorithm. Employing the symplectic integrators for MD algorithms, there is a conserved quantity which is close to Hamiltonian. Therefore, we can perform a MD simulation more stably than by conventional nonsymplectic algorithms. We applied this algorithm to a TIP3P pure water system at 300 K and compared the time evolution of the Hamiltonian with those by the nonsymplectic algorithms. We found that the Hamiltonian was conserved well by the symplectic algorithm even for a time step of 4 fs. This time step is longer than typical values of 0.5-2 fs which are used by the conventional nonsymplectic algorithms.