The S$_0$(0) structure in highly compressed hydrogen and the orientational transition

TL;DR

This study calculates the rotational S$_0$(0) frequencies in high-pressure solid para-hydrogen, revealing structural changes and potential quantum property implications at the phase transition.

Contribution

It provides a detailed theoretical analysis of the S$_0$(0) structure and its density-dependent behavior in compressed hydrogen, including convergence validation and comparison with experimental data.

Findings

Increase in lattice constant ratio c/a and internuclear distance with pressure

Decrease in anisotropic intermolecular potential due to charge transfer

Structural parameters at phase transition inform quantum property calculations

Abstract

A calculation of the rotational S$_0$(0) frequencies in high pressure solid para-hydrogen is performed. Convergence of the perturbative series at high density is demonstrated by the calculation of second and third order terms. The results of the theory are compared with the available experimental data to derive the density behaviour of structural parameters. In particular, a strong increase of the value of the lattice constant ratio $c/a$ and of the internuclear distance is determined. Also a decrease of the anisotropic intermolecular potential is observed which is attributed to charge transfer effects. The structural parameters determined at the phase transition may be used to calculate quantum properties of the rotationally ordered phase.