Use of Density Functional Methods To Compute Heats of Reactions

摘要

The use of density functional procedures for computing bond dissociation energies, heats of chemical reactions, and heats of formation is examined and discussed. The DF/B3P86/6-31+G~** combination of functionals and basis set has been found to be quite effective for the first two purposes, and is being extended to heats of formation, although these are presently being obtained with good accuracy at the DF/BP86/6-31G~** level. The decomposition of the energetic compound ammonium dinitramide is considered in some detail. It is suggested that the initial step may be sublimation to NH_3 + HN(NO_2)_2, followed by loss of NO_2 from either HN(NO_2)_2 or its tautomer O_2N-NN(O)OH. Computed #DELTA#H(298K) are listed for 32 possible intermediate steps.