Analysis of $\alpha $-phase RDX vibrational lattice modes under hydrostatic pressure

Calculations employing density functional theory are performed on $\alpha $-phase RDX using the all-electron CRYSTAL06 program. The lowest frequency infrared active lattice modes are investigated as a function of hydrostatic pressure from ambient conditions up to 3 GPa. The strength of coupling between lattice and molecular modes as a function of pressure is examined. The anharmonic deviation of each mode from simple harmonic behavior as a function of pressure is also illustrated.