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arXiv · 2507.17536

Hydrogen modes in KH$_2$PO$_4$ under pressure from ab initio calculation and inelastic neutron scattering

V. A. Abalmasov·A. S. Ivanov·R. A. Sadykov·A. V. Belushkin
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Abstract

The nature of the phonon triplet in the region of OH-stretching modes in hydrogen-bonded materials is often explained by the interplay of OH-stretching modes and combinations and overtones of OH-bending modes. In order to elucidate the both contributions in KH$_2$PO$_4$ (KDP), we compare the pressure dependence of the OH-bending and stretching modes from ab initio calculation and inelastic neutron scattering (INS) measurements. The ab initio calculation predicts a hardening of OH-bending modes and a softening of OH-stretching modes with pressure. At the same time, INS measurements in the region of OH-stretching modes indicate a hardening of the phonon triplet together with the bending modes. This means that this triplet in INS measurements is mainly due to combinations and overtones of OH-bending modes, while the intensity of OH-stretching modes appears to be relatively low. This conclusion may also apply to other hydrogen-bonded materials.

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V. A. Abalmasov, A. S. Ivanov, R. A. Sadykov, A. V. Belushkin. 2025-07-23. Hydrogen modes in KH$_2$PO$_4$ under pressure from ab initio calculation and inelastic neutron scattering. https://arxiv.org/abs/2507.17536

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