Atom Equivalent Energies for the Rapid Estimation of the Heat of Formation of Explosive Molecules from Density Functional Tight Binding Theory

Atom equivalent energies have been
derived from which the gas-phase
heat of formation of explosive molecules can be estimated from fast,
semiempirical density functional tight binding total energy calculations.
The root-mean-square deviation and maximum deviation of the heats
of formation from the experimental values for the set of 45 energetic
molecules compiled by Byrd and Rice [J. Phys. Chem. A, 2006, 110, 1005–1013] are
10.4 and 25.5 kcal/mol, respectively, using 4 atom equivalent energies
and 7.4 and 15.0 kcal/mol, respectively, using 7 atom equivalent energies.
These errors are around a factor of 2–3 larger than those obtained
from density functional theory calculations but are smaller than those
obtained from other semiempirical electronic structure methods. Heats
of formation calculated with density functional tight binding theory
using the 4 and 7 atom equivalent energies, the Byrd and Rice scheme,
and the atom pair contribution method for a new set of 531 energetic
molecules that contain only carbon, hydrogen, nitrogen, and oxygen
are provided.