Accelerating ab initio Molecular Dynamics and Probing the Weak Dispersive Forces in Dense Liquid Hydrogen

Area of Science:

• Computational Physics
• Quantum Chemistry
• Materials Science

Background:

• Simulating quantum and classical particles at finite temperatures often requires extensive computational time due to long autocorrelation times.
• Accurate modeling of materials under extreme conditions, such as high-pressure hydrogen, is crucial for understanding their properties and phase behavior.

Purpose of the Study:

• To introduce a novel ab initio molecular dynamics method that significantly reduces simulation autocorrelation times.
• To demonstrate the method's accuracy and efficiency in sampling for both classical and quantum systems.
• To determine the phase diagram of high-pressure hydrogen, particularly its liquid-liquid phase transition (LLT), with unprecedented simulation lengths.

Main Methods:

• Implementation of a modified first-order Langevin dynamics using a position-dependent acceleration matrix (S).
• Application to Lennard-Jones models for validation of sampling accuracy and speed-up.
• Integration with a quantum Monte Carlo (QMC) based wave function approach for quantum simulations.

Main Results:

• The proposed method dramatically reduces autocorrelation times, enabling simulations far exceeding typical lengths.
• Equilibration is achieved in a few hundred steps, even near the liquid-liquid phase transition (LLT).
• The LLT in high-pressure hydrogen is found to be consistent with recent density functional theory predictions that include long-range dispersive forces.

Conclusions:

• The developed ab initio molecular dynamics method offers a significant advancement in simulating complex systems efficiently.
• The findings provide new insights into the phase diagram of high-pressure hydrogen, particularly the LLT.
• This method has broad applicability for studying various classical and quantum systems at finite temperatures.