title: Hydrogen bond symmetrization and superconducting phase of HBr and HCl under high pressure: An ab initio study.
abstract: Ab initio calculations are performed to probe the hydrogen bonding, structural, and superconducting behaviors of HBr and HCl under high pressure. The calculated results show that the hydrogen bond symmetrization (Cmc2(1)-->Cmcm transition) of HBr and HCl occurs at 25 and 40 GPa, respectively, which can be attributed to the symmetry stretching A(1) mode softening. After hydrogen bond symmetrization, a pressure-induced soft transverse acoustic phonon mode of Cmcm phase is identified and a unique metallic phase with monoclinic structure of P2(1)/m (4 molecules/cell) for both compounds is revealed by ab initio phonon calculations. This phase preserves the symmetric hydrogen bond and is stable in the pressure range from 134 to 196 GPa for HBr and above 233 GPa for HCl, while HBr is predicted to decompose into Br(2)+H(2) above 196 GPa. Perturbative linear-response calculations predict that the phase P2(1)/m is a superconductor with T(c) of 27-34 K for HBr at 160 GPa and 9-14 K for HCl at 280 GPa.
authors: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, People's Republic of China.
authors: Defang
authors: D
authors: Duan
authors: Fubo
authors: F
authors: Tian
authors: Zhi
authors: Z
authors: He
authors: Xing
authors: X
authors: Meng
authors: Liancheng
authors: L
authors: Wang
authors: Changbo
authors: C
authors: Chen
authors: Xiusong
authors: X
authors: Zhao
authors: Bingbing
authors: B
authors: Liu
authors: Tian
authors: T
authors: Cui
mesh_terms: D004553:Electric Conductivity; D018054:Hydrobromic Acid / Q000737:chemistry*; D006851:Hydrochloric Acid / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D044367:Phase Transition; D011312:Pressure; D011789:Quantum Theory
chemical_list: D018054:Hydrobromic Acid; D006851:Hydrochloric Acid