Fundamental high pressure calibration from all-electron quantum Monte Carlo calculations

TL;DR

This paper introduces an all-electron quantum Monte Carlo method for solids, providing a highly accurate high-pressure calibration based on the equation of state of cubic boron nitride, applicable up to 900 GPa.

Contribution

It develops a pseudopotential-free QMC approach for solids and constructs a primary high-pressure calibration that improves accuracy and reduces systematic errors in experimental pressure measurements.

Findings

Achieved high-accuracy EOS calibration up to 900 GPa

Computed anharmonic Raman frequency shifts with QMC

Provided a benchmark for pseudopotential accuracy

Abstract

We develop an all-electron quantum Monte Carlo (QMC) method for solids that does not rely on pseudopotentials, and use it to construct a primary ultra-high pressure calibration based the equation of state of cubic boron nitride(c-BN). We compute the static contribution to the free energy with QMC, and obtain the phonon contribution from density functional theory, yielding a high-accuracy calibration up to 900 GPa usable directly in experiment. Furthermore, we compute the anharmonic Raman frequency shift with QMC as a function of pressure and temperature, allowing optical pressure calibration in table-top experiments. In contrast to present experimental approaches, small systematic errors in the theoretical EOS do not increase with pressure, and no extrapolation is needed. This all-electron methodology is generally applicable to first-row solids, and can be used to provide a new reference for ab initio calculations of solids and to benchmark pseudopotential accuracy.