Phonon anharmonicity and the pressure dependence of phonon lifetime for solid nitromethane by ab initio calculations

Abstract

Phonon anharmonicity is important for energy transfer in energetic materials. Here we have investigated the vibrational anharmonicity including phonon lifetime, mode Grüneisen parameters and lattice thermal conductivity of solid nitromethane using first-principles calculations combining Boltzmann transport equation theory. The calculated structural and vibrational properties of solid nitromethane agree well with experimental results. It’s found that the CN stretching mode among all phonons has the longest lifetime with 99.3 ps at ambient condition. It’s worth noting that this would allow the vibrational energy to reside in this mode for a long time, leading to the formation of “hot” chemical bond and further its rapture. This is consistent with the previous report that the breakage of CN bond may be the initial reaction in nitromethane. The results also show the lifetimes of internal modes are generally higher than those of lattice modes. And the mode Grüneisen parameters indicate that the lattice modes are much more sensitive to the volume change than internal modes. Moreover, the lattice thermal conductivity of solid nitromethane shows obvious anisotropy. Finally, the influence of hydrostatic pressure on the phonon lifetime of solid nitromethane was also calculated and discussed.