High-pressure phase transitions of solid HF, HCl, and HBr: An ab initio evolutionary study

摘要

Using ab initio evolutionary methodology for structure predictions, we investigated the high-pressure phase diagram for solid-state HF, HCl, and HBr at zero temperature. The ambient-pressure chain-type Cmc2_1 structure and sequent high-pressure symmetric hydrogen-bonded Cmcm structure were successfully reproduced by structural simulations with the only known information of chemical compositions. We have also presented insight into the underlying mechanism of hydrogen-bond symmetrization at the Cmc2_1→ Cmcm transformation, by analysis of electron localization functions, potential wells, and zone-center phonons with pressure. At higher pressures, it was predicted that HF transforms from the Cmcm phase to another chain-type Pnma structure at ～ 143 Gpa while the post-Cmcm phase of HCl and HBr adopts an intriguing triclinic P1 structure at above 108 Gpa and 59 Gpa, respectively, which consists of nearly planar squares resembling the ambient phase of HI. The newly predicted high-pressure phases of these halides all contain symmetric hydrogen bonds and satisfy lattice dynamical stability. As for the earlier proposed dissociation of HBr, we found that this can only occur at rather high pressures (above 120 Gpa) with the formation of monatomic Br and solid H_2.