Structural and thermodynamic properties of two polymorphic modifications of the insensitive high explosive 5-nitro-2,4-dihydro-1,2,4-triazol-3-one (NTO) under finite pressures and temperatures from ab initio calculations

Abstract

The effect of finite pressures and temperatures on the structural and thermodynamic properties of two polymorphic modifications of a promising insensitive high explosive 5-nitro-2,4-dihydro-1,2,4-triazol-3-one (NTO) was investigated from first principles. The equilibrium cell parameters and isotherms at zero and finite temperatures were determined as well as the vibrational spectra of the two phases. For β-NTO, a structural change was discovered at about 17.5 GPa. Calculations of the properties of the most stable low-symmetry α-phase were performed. A quasi-harmonic approximation was used to determine the bulk sound velocities in the polymorphic modifications of NTO under finite temperatures and evaluate their relative stability.