Equation of State and First Principles Prediction of the Vibrational Matrix Shift of Solid Parahydrogen

TL;DR

This paper presents a first-principles simulation of solid parahydrogen's equation of state, structural stability, and vibrational matrix shift, achieving good agreement with experimental data and providing novel predictive insights.

Contribution

It introduces a highly accurate first-principles approach to predict the vibrational matrix shift and EOS of solid parahydrogen, including the first a priori prediction of the matrix shift.

Findings

Hcp structure is more stable than fcc, consistent with experiments.

The EOS and compressibility match previous simulations and experiments.

First-ever first-principles prediction of vibrational matrix shift agrees with experimental data.

Abstract

We generate the equation of state (EOS) of solid parahydrogen using a path-integral Monte Carlo (PIMC) simulation based on a highly accurate first-principles adiabatic hindered rotor (AHR) potential energy curve for the parahydrogen dimer. The EOS curves for the fcc and hcp structures of solid parahydrogen near the equilibrium density show that the hcp structure is the more stable of the two, in agreement with experiment. To accurately reproduce the structural and energy properties of solid parahydrogen, we eliminated by extrapolation the systematic errors associated with the choice of simulation parameters used in the PIMC calculation. We also investigate the temperature dependence of the EOS curves, and the invariance of the equilibrium density with temperature is satisfyingly reproduced. The pressure as a function of density, and the compressibility as a function of pressure, are both calculated using the obtained EOS and are compared with previous simulation results and experiments. We also report the first ever a priori prediction of a vibrational matrix shift from first-principles two-body potential functions, and its result for the equilibrium state agrees well with experiment.