Complete Equations of State for Cyclotetramethylene Tetranitramine

Complete equations of state for the volumetric deformation of the beta-polymorph of cyclotetramethylene tetranitramine (beta-HMX) have been derived from its Helmholtz free energy. Dispersion-corrected density functional theory calculations were used to compute the dependence of the frequencies of the vibrational normal modes on specific volume. The normal mode frequencies were used directly to generate both a tabular equation of state and an approximate model where the sum over normal mode frequencies is replaced by a set of five Debye models. Both the tabular and Debye model-based equations of state use the same cold curve, which is parameterized to the isothermal compression data of Yoo and Cynn [C. S. Yoo and H. Cynn, J. Chem. Phys., 1999, 111, 10229]. The two equations of state are applied to the calculation of the thermophysical properties of beta-HMX required for continuum-level hydrodynamic simulations and are compared in detail.

Automated summary

Complete equations of state for the volumetric deformation of beta-HMX have been derived from its Helmholtz free energy, with dispersion-corrected density functional theory calculations used to compute normal mode frequencies. The calculated frequencies were used to generate tabular and approximate models for the equations of state, both based on a set of Debye models. The resulting equations were applied to calculate the thermophysical properties of beta-HMX and compared in detail.