Polarization and Strong Infra-Red Activity in Compressed Solid Hydrogen

TL;DR

This paper investigates the IR activity in compressed solid hydrogen, revealing large dynamic charges and the inadequacy of traditional models due to molecular overlap at high pressures.

Contribution

It applies Berry's phase approach to calculate polarization in compressed hydrogen, highlighting the importance of molecular overlap on IR activity and challenging classical models.

Findings

Large, anisotropic dynamic charges in compressed hydrogen

Strong IR-active vibron modes observed

Overlap between molecules significantly affects polarization calculations

Abstract

Under a pressure of ~150 GPa solid molecular hydrogen undergoes a phase transition accompanied by a dramatic rise in infra-red absorption in the vibron frequency range. We use the Berry's phase approach to calculate the electric polarization in several candidate structures finding large, anisotropic dynamic charges and strongly IR-active vibron modes. The polarization is shown to be greatly affected by the overlap between the molecules in the crystal, so that the commonly used Clausius-Mossotti description in terms of polarizable, non-overlapping molecular charge densities is inadequate already at low pressures and even more so for the compressed solid.