First principle studies of ammonium chloride under high pressure

We performed a thorough high-pressure structural exploration of ammonium chloride up to 300 GPa by ab initio calculations. Two new phases, namely, P2(1)/m and Cmma, were predicted to be stable within the pressure ranges of 71–107 and 107–300 GPa, respectively. Like the known phase IV and V, the two new phases preserve alternate ammonium and chloride ions layer structures. The Bader charge analysis indicated that the numbers of electrons that N atoms get abruptly increased in the P2(1)/m phase. We also calculated the band gap and the variations in interatomic distances with pressure, and found the band gaps of two new phases decrease with increasing pressure and do not close up to 300 GPa.