Predicting heats of detonation using quantum mechanical calculations

Heats of detonation of pure explosives and explosive formulations are predicted using quantum mechanical (QM) information generated for isolated molecules. The methodology assumes that the heat of detonation of an explosive compound of composition CaHbNcOd can be approximated as the difference between the heats of formation of the detonation products and that of the explosive, divided by the formula weight of the explosive. Two sets of decomposition gases were assumed: the first corresponds to the H2OCO2 arbitrary [J. Chem. Phys. 48 (1968) 23]. The second set assumes that the product composition gases consist almost solely of H2, N2, H2O, CO, and CO2. The heats of formation used in this method are predicted using equations that convert QM information for an isolated energetic molecule to condensed phase heats of formation. Solid phase heats of formation predicted using the methods described herein have a root mean square (rms) deviation of 13.7 kcal/mol from 72 measured values (corresponding to 30 molecules). For the calculations in which the first set of decomposition gases is assumed, predicted heats of detonation of pure explosives with the product H2O in the gas phase have a rms deviation of 0.138 kcal/g from experiment; results with the product H2O in the liquid state have a rms deviation of 0.116 kcal/g from experiment. Predicted heats of detonation assuming the second set of decomposition gases have a rms deviation from experiment of 0.098 kcal/g. Heats of detonation for explosive formulations were also calculated, and have a rms deviation from experiment of 0.058 kcal/g.