Decomposition of solid hydrogen bromide at high pressure

The stability of different stoichiometric H${}_n$Br ($n$=1-7) compounds under pressure are extensively studied using density functional theory calculations. Five new energetically stable stoichiometries of H${}_2$Br, H${}_3$Br, H${}_4$Br, H${}_5$Br, and H${}_7$Br were uncovered at high pressure. The results show that HBr is stable below 64 GPa, then decomposes into new compound H${}_2$Br and Br${}_2$ molecular crystal. For H${}_2$Br and H${}_3$Br compounds, they were found to become stable above 30 GPa and 8 GPa, respectively. In addition, we accidentally discovered the triangular H${}_3^{+}$ species in H${}_5$Br compounds at 100 GPa. Further electron-phonon coupling calculations predicted that hydrogen-rich H${}_2$Br and H${}_4$Br compounds are superconductors with critical temperature of superconductivity $T_c$ of 12.1 K and 2.4 K at 240 GPa, respectively.