Direct free energy calculation from ab initio path integral Monte Carlo simulations of warm dense matter

TL;DR

This paper presents a highly accurate ab initio path integral Monte Carlo method to directly compute free energies of warm dense matter systems, avoiding common approximations and applicable to various quantum systems.

Contribution

The authors develop a novel PIMC approach that estimates free energies directly without nodal restrictions, applicable to inhomogeneous and diverse quantum systems.

Findings

Accurate free energy calculations for warm dense matter systems.

Method applicable to inhomogeneous electronic systems with external potentials.

Potential to benchmark and improve density functional theory methods.

Abstract

We carry out highly accurate \emph{ab initio} path integral Monte Carlo (PIMC) simulations to directly estimate the free energy of various warm dense matter systems including the uniform electron gas and hydrogen without any nodal restrictions or other approximations. Since our approach is based on an effective ensemble in a bosonic configuration space, it does not increase the computational complexity beyond the usual fermion sign problem. Its application to inhomogeneous cases such as an electronic system in a fixed external ion potential is straightforward and opens up the enticing possibility to benchmark density functional theory and other existing methods. Finally, it is not limited to warm dense matter, and can be applied to a gamut of other systems such ultracold atoms and electrons in quantum dots.