Theoretical investigation of vibrational and electronic properties of HMX crystal under uniaxial compression.

Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is a typical energetic molecular crystal with excellent detonation performance and good thermal stability, has been widely used in military and civilian purposes. In this work, the vibrational properties of HMX combined with structure and electronic properties are studied to understand its pressure response against uniaxial compressions. The calculated eigenvalues of stress tensors show significant anisotropy of intermolecular interactions. Especially, the direction of shear stressτxyandτxzin [100] compression have an abrupt change nearV/V0= 0.84. Further, Raman spectra under each uniaxial compression are simulated to inspect the molecular configuration of HMX. Compared to the blue shifts of [010] and [001] orientations, the discontinuous Raman shifts of atV/V0= 0.86-0.84 in [100] orientation suggest that HMX would undergoes a possible structural transformation at the pressure of 6.82-9.15 GPa. Structural analysis implies that the subtle rotation of NO2group is changed by intermolecular interactions of HMX. Moreover, the abnormal evolution of band gap is observed atV/V0= 0.84 in [100] orientation, which is associated with the structure modification of HMX. Overall, the compression behaviors of HMX under uniaxial compressions would provide a useful insight for the actual shock compression conditions.