Structures of solid hydrogen at 300K

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Abstract

We present simulated X-ray diffraction patterns (XRD) from molecular dynamics studies of phase transformations in hydrogen at room temperature. Phase changes can be easily identified in simulation, by directly imaging the atoms and measuring correlation functions. We show that the room temperature XRD patterns for hydrogen phases I, III, IV and V are very similar. The
signature of the transformations in XRD are weak peaks and superlattice re
ections denoting symmetry-breaking from the hcp Phase I, and a pronounced change in the c/a ratio. The XRD patterns implied by molecular dynamics calculations are very different from those arising from the static minimum enthalpy structures found by structure searching. Simulations also show that within Phase I, the molecules becomes increasingly confined to the basal plane and suggest the possibility of an unusual critical point terminating the Phase I-III boundary line. With these results, we propose a paradigm shift { that the predictions from DFT calculations should be seen as the most likely hypothesis. Specifically, we show that recent experimental results support the picture advanced by molecular dynamics simulations, and are inconsistent with the interpretation of an isostructural hcp transformation.
Original languageEnglish
Article number094104
JournalPhysical Review B
Volume101
Issue number9
DOIs
Publication statusPublished - 18 Mar 2020

Keywords

  • cond-mat.mtrl-sci

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