Response of the structure and vibrational modes of nitromethane to pressure

First-principles calculations were implemented to study the chemical evolutions of solid nitromethane under pressure up to 20 GPa. The breakpoints of c lattice, bond length/angle, intermolecular interaction and band gap at 6 GPa mean the rotation of methyl, while no phase transition generates by verifying with Raman spectra here. Another breakpoint around 14 GPa can be explained by the inconsistency of the corresponding vibration movement of peaks. Moreover, we explain the band gap mutation caused by methyl rotation.