title: Ab initio equation of state of the organic molecular crystal: beta-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine.
abstract: We apply a simple strategy for calculating from first principles a thermodynamically complete equation of state for molecular crystals using readily available quantum chemistry techniques. The strategy involves a combination of separate methods for the temperature-independent mechanical compression and the thermal vibrational contributions to the free energy. A first principles equation of state for beta-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (beta-HMX) has been calculated for temperatures between 0 and 400 K and for specific volumes from 0.42 to 0.55 cm(3)/g, corresponding to relative volumes from 0.8 to 1.03. The calculated 300 K isotherm agrees very well with the experimentally measured pressure-volume relation. We also discuss thermodynamic properties of the material such as the volumetric thermal expansion coefficient, the Gruneisen parameter, and the specific heat (1.0 kJ/kg/K at 300 K and atmospheric pressure). The developed computational approach exhibits a reliable predictive power and is easily transferable to other molecular materials.
authors.affiliation: Research and Technology Department, Naval Surface Warfare Center, Indian Head, Maryland 20640, USA.
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Zerilli
authors.forename: Maija M
authors.initials: MM
authors.lastname: Kuklja
mesh_terms: D001392:Azocines / Q000737:chemistry*; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D011789:Quantum Theory; D013696:Temperature; D013816:Thermodynamics; D014732:Vibration
chemical_list: D001392:Azocines; C007950:octogen