First-principles study of structural, hydrogen bonds and mechanical properties of α-RDX under hydrostatic compression

Abstract

The mechanical response of cyclotrimethylene trinitramine (RDX) under pressure loading is closely correlated with the structural deformation and chemical decomposition. The structural, hydrogen bonds (HBs) and mechanical properties of α-RDX under hydrostatic compression between 0 and 4 GPa have been studied using dispersion corrected density functional theory (DFT-D). The oxygen atoms in the E branch (AAE configuration) form important intermolecular HBs with pressure increasing, wherein the bond order of the HB marked as O3∙∙∙H5-C3 reaches up to 0.0716 (∼1.8 times of the intramolecular bonds) at 4 GPa. This HB directly prompts the pressure-dependent increase of Young’s modulus in y direction. α-RDX keeps mechanically stable below 4 GPa, while it shows a pressure-induced ductility owing to deformation tendency in (010) plane (i.e., ac plane). Finally, the pressure-dependent anisotropy, sound velocities and Debye temperature are also discussed based on the calculated mechanical moduli.