NVU dynamics. III. Simulating molecules at constant potential energy

TL;DR

This paper extends geodesic molecular dynamics at constant potential energy to simulate molecules with rigid bonds, demonstrating that NVU dynamics aligns with NVE dynamics in the thermodynamic limit for molecular systems.

Contribution

It introduces an NVU algorithm for molecular systems with rigid bonds, maintaining key physical constraints and showing equivalence to NVE dynamics.

Findings

NVU algorithm conserves potential energy and bond lengths.

Results match Nose-Hoover NVT and NVE dynamics.

NVU dynamics becomes equivalent to NVE in the thermodynamic limit.

Abstract

This is the final paper in a series that introduces geodesic molecular dynamics at constant potential energy. This dynamics is entitled NVU dynamics in analogy to standard energy-conserving Newtonian NVE dynamics. In the first two papers [Ingebrigtsen et al., J. Chem. Phys. 135, 104101 (2011); ibid, 104102 (2011)], a numerical algorithm for simulating geodesic motion of atomic systems was developed and tested against standard algorithms. The conclusion was that the NVU algorithm has the same desirable properties as the Verlet algorithm for Newtonian NVE dynamics, i.e., it is time-reversible and symplectic. Additionally, it was concluded that NVU dynamics becomes equivalent to NVE dynamics in the thermodynamic limit. In this paper, the NVU algorithm for atomic systems is extended to be able to simulate geodesic motion of molecules at constant potential energy. We derive an algorithm for simulating rigid bonds and test this algorithm on three different systems: an asymmetric dumbbell model, Lewis-Wahnstrom OTP, and rigid SPC/E water. The rigid bonds introduce additional constraints beyond that of constant potential energy for atomic systems. The rigid-bond NVU algorithm conserves potential energy, bond lengths, and step length for indefinitely long runs. The quantities probed in simulations give results identical to those of Nose-Hoover NVT dynamics. Since Nose-Hoover NVT dynamics is known to give results equivalent to those of NVE dynamics, the latter results show that NVU dynamics becomes equivalent to NVE dynamics in the thermodynamic limit also for molecular systems.