Ab initio simulation of defects in energetic materials: Hydrostatic compression of cyclotrimethylene trinitramine

An isotropic compression of both the perfect solid cyclotrimethylene trinit ramine (C3H6N6O6), also known as RDX, and of the solid containing vacancies is simulated using the ab initio Hartree-Fock method combined with two dif ferent crystal models: a periodic (band structure) and a molecular cluster. We show that an external pressure causes a significant decrease of the opt ical gap for both the perfect material and the crystal with vacancies. The solid RDX is found to be highly compressible; a pure crystal could be compr essed to 57% of its equilibrium volume, whereas crystals containing vacanci es are even more compressible. The critical pressure necessary for the insu lator-metal transition is also predicted. It is shown that the voids presen t in a real RDX solid lower the metallization pressure by about 30%. Theore tical results are in close agreement with the experimental data on solid an d porous RDX. The influence of defects present in the crystal and the relat ion to control of the sensitivity to detonation are discussed in detail. (C ) 1999 American Institute of Physics. [S0021-8979(99)09520-1].