High-pressure behavior of crystalline FOX-7 by density functional theory calculations

1,1-Diamino-2,2-dinitroethylene (C2H4N4O4, FOX-7) is a newly found energetic materials with high performance and low sensitivity. We performed density functional theory (DFT) calculations within local density approximation (LDA) as well as generalized gradient approximation (GGA) to simulate the structural and electronic properties of FOX-7 crystal under high-pressure up to 4 GPa. Due to the insufficient treatment of weakly intermolecular interaction, LDA underestimates the lattice parameters and volume, while GGA overestimates them. It is interesting to find that a mixing of LDA and GGA results of lattice properties can lead to fairly good agreement with experiments. Examination of pressure-induced changes of molecular geometry shows that the C–N bonds are most sensitive under compression. The change of band gap as function of external pressure was also discussed.