Path integral Brownian chain molecular dynamics: A simple approximation of quantum vibrational dynamics

Area of Science:

• Computational Chemistry
• Quantum Dynamics
• Molecular Simulation

Background:

• Path integral (PI) simulations face challenges with chain resonance and curvature.
• Accurate quantum vibrational dynamics are crucial for understanding molecular behavior.

Purpose of the Study:

• To introduce Brownian chain molecular dynamics (BCMD) as an approximate approach to quantum vibrational dynamics.
• To overcome limitations of existing path integral methods.

Main Methods:

• BCMD randomizes non-centroid velocity in path integral molecular dynamics.
• It combines Newton's and Langevin equations for centroid and non-centroid variables.
• On-the-fly ab initio simulations were performed for water clusters.

Main Results:

• BCMD demonstrates correct short-time Kubo-transformed correlation functions and conserves time symmetry.
• It achieves correct high-temperature/classical limits and harmonic oscillator properties.
• The method avoids the zero-point leakage problem observed in other PI approaches.

Conclusions:

• BCMD provides a robust and accurate method for quantum vibrational dynamics.
• The approach is validated through simulations of molecular models, liquid water, and protonated water clusters.