Equation of State for Single Crystal 3,3′-Diamino-4,4′-azoxyfurazan

Abstract

Tabular and Debye equations of state (EoS) have been developed for single crystal 3,3′-diamino-4,4′-azoxyfurazan (DAAF) from density functional theory calculations of the static lattice energy (i.e., the cold curve) and the dependence of the frequencies of the vibrational normal modes on specific volume. The cold curves are represented by the three parameter MACAW reference curve developed by Lozano and Aslam. The thermal ionic contributions to the Helmholtz free energy are either interpolated and tabulated in a SESAME table or represented by a sum of five Debye models with volume-dependent Debye temperatures. The agreement between the two EoS and with the available experiments is generally good. We provide predictions for the Hugoniot locus up to 40 GPa and the temperature dependence of the heat capacity up to 2000 K. Tensors of second and third order elastic constants calculated using density functional theory, which enable the calculation of the thermoelastic free energy of DAAF under large lattice strains that probe the anharmonicity of the interatomic forces, are also reported.