Abstract

The structural, dynamical, and electronic properties of solid HBr at high pressure are investigated using the ab initio constant pressure molecular dynamics method. A detailed analysis of the orientational distribution, and the reorientational and vibrational dynamics of the disordered phase I at ambient temperature showed that this phase can be described as a rotator phase with fluctuating hydrogen bonds up to pressures well over 10 GPa. We predict that the disorder at higher densities leads to cooperative proton-transfer dynamics. The approach to hydrogen-bond symmetrization is studied in phase I and the high pressure ordered phase III. The simulation results for phase III also indicate that this phase develops dielectric instabilities at high density. At pressures over 40 GPa we observe spontaneous formation of H2 with rearrangement of the Br lattice from fcc to hcp. The chemical reactivity is rationalized in terms of the electronic structure under conditions of near symmetrical hydrogen bonding.

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