Ab initio molecular dynamics simulation of vibrational energy redistribution of selective excitation of C-H stretching vibrations for solid nitromethane.

Vibrational energy redistribution (VER) of energetic materials plays an important role in transferring the injected energy to the hot spots, but it is extremely challenging to understand the mechanism of VER from experimental or theoretical studies. Here, we combined nonequilibrium molecular dynamics with density functional theory to study the processes of VER for solid nitromethane after the selective excitation of the C-H stretching vibration. The VER processes are traced by monitoring the normal-mode kinetic energies of both excited and unexcited vibrations. To explore the underlying VER mechanism, we also analyzed the spectral energy density for the normal mode, obtained from the squared modulus of the short-time Fourier transition of their normal mode momentum. The results showed that the simulated VER progress was reproduced well compared with the previous 3D IR-Raman experiments of liquid nitromethane. Interestingly, the symmetric dependence of the coupling mechanism between the normal modes has been found.