A First Principles Density Functional Study of Crystalline FOX-7 Chemical Decomposition Process under External Pressure

摘要

We report on a first principles analysis of chemical decomposition reaction in a crystalline FOX-7 (l,l-diamino-2,2-dinitro-ethylene)molecule,which is a good candidate for insensitive energetic materials.Our calculations are based on variable-cell shape methods under pressure,density functional theory with localized numerical orbital and pseudopotential,together with ab initio biasing molecular dynamics.The calculated crystal structure and equation of state (pressure vs.volume)up to 8 GPa agrees well with the corresponding experimental data.A chemical decomposition by intermolecular hydrogen transfer is found at higher pressure.This decomposition appears to be driven by a weakening in the chemical hardness.This suggests that the molecular HOMO and LUMO orbital energy difference is decreased when intermolecular hydrogen transfers occur,and for the FOX-7 crystal the band gap is narrowed with increasing external pressure.