Structural and Vibrational Properties of Crystalline β‐Octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine at High Temperatures: Ab Initio Molecular Dynamics Studies

Abstract

We investigated the temperature influence on the structural and vibrational properties of β-HMX (β-octahydro-1,3,5,7tetranitro-1,3,5,7-tetrazocine) by using a combination of ab initio molecular dynamics and density function theory. The results indicate that the lattice constants and unit-cell volume of HMX do not present obvious temperature effects. Most of the vibrational modes display similar hardening trend under the temperatures, suggesting that the crystal transformation of HMX under heat is through this displacement. The dependence of Infra-red spectra on the temperature presents red-shifted and a little decrease in the intensity of lattice vibration. This may suggest that there is a new bond formed or an old bond broken in the system if the temperature is higher than 873 K. The intensity of ratting mode caused by volumetric contraction and Raman are obviously much larger than that of the crystalline HMX at 0 K and the lattice vibrations are blueshifted. It demonstrates that the lattice vibrations are much more drastic. It is found that the deformation vibrations of cycle and nitro group are milder at relatively higher temperatures. This suggests that the cycle space becomes small enough to influence the HMX vibrations.[a] Dr.