Interaction Picture Density Matrix Quantum Monte Carlo

TL;DR

This paper introduces an improved density matrix quantum Monte Carlo method using the interaction picture, enabling more accurate simulations of interacting fermions like the warm dense uniform electron gas at finite temperatures.

Contribution

The study demonstrates the advantages of the interaction picture in DMQMC for fermionic systems and provides benchmark results for a four-electron system in the warm dense regime.

Findings

Interaction picture enhances DMQMC efficiency for fermions.

Finite temperature basis set errors can be effectively extrapolated.

Benchmark results align with previous studies where available.

Abstract

The recently developed density matrix quantum Monte Carlo (DMQMC) algorithm stochastically samples the N -body thermal density matrix and hence provides access to exact properties of many-particle quantum systems at arbitrary temperatures. We demonstrate that moving to the interaction picture provides substantial benefits when applying DMQMC to interacting fermions. In this first study, we focus on a system of much recent interest: the uniform electron gas in the warm dense regime. The basis set incompleteness error at finite temperature is investigated and extrapolated via a simple Monte Carlo sampling procedure. Finally, we provide benchmark calculations for a four-electron system, comparing our results to previous work where possible.