The first principle studies of the structural and vibrational properties of solid -HMX under compression

The structural, vibrational and electronic properties of -octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (-HMX) crystal under high pressure up to 40 GPa have been studied using density functional theory (DFT). The pressure dependences on the cell volume, lattice constants, and molecular geometry of solid -HMX are presented and discussed. It is found that the N-N bonds are significantly reduced under compression, which may be of importance for initial decomposition. Based on the optimized crystal structures, the vibrational frequencies for the internal and lattice modes of the -HMX crystal at ambient and high pressures are computed, and the pressure-induced frequency shifts of these modes are discussed.