Hydrogen mean force and anharmonicity in polycrystalline and amorphous ice

TL;DR

This study uses neutron scattering to analyze hydrogen mean force in amorphous and polycrystalline ice, revealing how anharmonicity and anisotropy affect the hydrogen-nucleus potential.

Contribution

It extends the mean force formalism to assess anharmonicity sensitivity in hydrogen effective potentials in different ice forms.

Findings

Amorphous ice exhibits greater anharmonicity than ice Ih.

Mean force shape is mainly influenced by potential anisotropy.

Data indicates increased anharmonicity in amorphous ice.

Abstract

The hydrogen mean force from experimental neutron Compton profiles is derived using deep inelastic neutron scattering on amorphous and polycrystalline ice. The formalism of mean force is extended to probe its sensitivity to anharmonicity in the hydrogen-nucleus effective potential. The shape of the mean force for amorphous and polycrystalline ice is primarily determined by the anisotropy of the underlying quasi-harmonic effective potential. The data from amorphous ice show an additional curvature reflecting the more pronounced anharmonicity of the effective potential with respect to that of ice Ih.