Computational prediction of standard gas, liquid, and solid-phase heats of formation and heats of vaporization and sublimation

We present a B3PW91/6-31G** computational procedure for predicting standard gas phase heats of formation at 298.15 K by finding Delta H for the process whereby the molecule is produced from its elements and then adding empirical atomic correction terms. Heats of vaporization and sublimation are estimated on the basis of the calculated electrostatic potential on the molecular surface. These results permit prediction of the standard liquid and solid-phase heats of formation. In comparison with experimental data, the average absolute deviations are as follows: for the heats of formation, gas phase, 2.6 kcal/mol; liquid phase, 2.4 kcal/mol; solid phase, 3.8 kcal/ mol; for the heats of vaporization, 2.0 kcal/mol; and for the heats of sublimation, 2.8 kcal/mol. Computed values of these properties are given for a number of compounds for which they are not available experimentally. (c) 2005 Wiley Periodicals, Inc. Int J Quantum Chem 105: 341-347, 2005.