Incorporating Nuclear Quantum Effects in Molecular Dynamics with a Constrained Minimized Energy Surface

TL;DR

This paper introduces a new molecular dynamics method that accurately incorporates nuclear quantum effects by evolving quantum nuclear positions classically on a constrained minimized energy surface, improving over existing approaches.

Contribution

The paper develops a theoretical foundation for CNEO-MD, enabling classical MD to include nuclear quantum effects through a constrained energy minimization framework.

Findings

CNEO-MD is more accurate than conventional classical MD.

CNEO-MD outperforms centroid MD and ring-polymer MD in vibrational descriptions.

The approach provides a new way to incorporate quantum effects efficiently.

Abstract

The accurate incorporation of nuclear quantum effects in large-scale molecular dynamics (MD) simulations remains a significant challenge. Recently, we combined constrained nuclear-electronic orbital (CNEO) theory with classical MD and obtained a new approach (CNEO-MD) that can accurately and efficiently incorporate nuclear quantum effects into classical simulations. In this Letter, we provide the theoretical foundation for CNEO-MD by developing an alternative formulation of the equations of motion for MD. In this new formulation, the expectation values of quantum nuclear positions evolve classically on an effective energy surface that is obtained from a constrained energy minimization procedure when solving for the quantum nuclear wave function, thus enabling the incorporation of nuclear quantum effects in classical MD simulations. For comparison with other existing approaches, we examined a series of model systems and found that this new MD approach is significantly more accurate than the conventional way of performing classical MD, and it also generally outperforms centroid MD and ring-polymer MD in describing vibrations in these model systems.