A new high-pressure polar phase of crystalline bromoform: a first-principles study

The high-pressure phases of bromoform at zero temperature have been investigated by first-principles pseudopotential plane-wave calculations based on the density functional theory. A new high-pressure polar phase, ε, with space group CC has been found after a series of simulated annealing and geometry optimizations. Our calculated enthalpies showed that the transition from β phase to γ phase occurs at 1 GPa, then the γ phase transforms to the ε phase at 90 GPa. In addition, the Br···Br and C-H···Br interactions are the key factors for the polar aggregation in the ε phase. Further calculations show that the insulate-metal transition in ε phase due to band overlap happens at ~130 GPa.