Enthalpies of formation from B3LYP calculations

We have Calculated the geometries, energies, and normal vibrations of 845 compounds containing the elements H, C, N, O, R Al, Si, R S, and Cl using hybrid density functional theory in order to investigate the accuracy of atom-additive schemes for predicting enthalpies of formation at 298 K. The results give a more realistic estimate of the accuracy of density functional calculations than some overoptimistic earlier correlations. We have also calculated atom-additive schemes for the zero-point energies and enthalpic corrections to the energies. Remarkably, it is not important to include the vibrational or rotational contributions, which can be estimated well within a purely Born-Oppenheimer regression model. (C) 2004 Wiley Periodicals, Inc.