Path Integral Calculations of the Hydrogen Hugoniot Using Augmented Nodes

TL;DR

This paper presents an advanced path integral Monte Carlo method with an optimized fixed-node approximation to accurately compute the hydrogen Hugoniot across a wide temperature range, improving previous models and enabling future chemical system simulations.

Contribution

Introduces an efficient finite-temperature fixed-node approximation combining free particle states and atomic orbitals for hydrogen, enhancing path integral simulations.

Findings

Hugoniot calculations agree with previous results at high temperatures

Smoothly connect to low-temperature gas gun results

Open new avenues for simulating other chemical systems

Abstract

We calculate the hydrogen Hugoniot using ab initio path integral Monte Carlo. We introduce an efficient finite-temperature fixed-node approximation for handling fermions, which includes an optimized mixture of free particle states and atomic orbitals. The calculated Hugoniot confirms previous fixed-node path integral calculations at temperatures around T=30,000 K and above, while approaching smoothly the low temperature gas gun results. The ability to optimize the free energy within the path integral opens many new possibilities for developing nodal density matrices for path integral simulations of other chemical systems.