Effect of Hydrostatic Compression on Structure and Properties of 2-Diazo-4,6- Dinitrophenol Crystal: Density Functional Theory Studies

The effect of hydrostatic pressure on the geometrical, electronic, and thermodynamic properties of the energetic material 2-diazo-4,6-dinitrophenol (DDNP) has been investigated by density functional theory periodic calculations. The crystal structure optimized by the local density approximation with the Ceperley–Alder exchange-correlation potential parametrized by Perdew and Zunger compares well with the experimental results at the ambient pressure. When the hydrostatic compression is exerted upon the DDNP crystal, the interatomic distances, bond angles, and dihedral angles of DDNP molecule change regularly with the increase in pressure except at 10, 59, and 66 GPa where the structural transformations occur. The same is true for the unit cell lattice parameters, density, total energy, band gap, density of states, and thermodynamic functions. When the pressure is below 10 GPa, DDNP molecule exists in the quinoid form ( I ). As the pressure is between 10 and 58 GPa, it has the cyclic azoxy form ( II ). In the range of 0–58 GPa, DDNP crystal is anisotropic.