ACCURATE THERMOCHEMISTRY FOR LARGER MOLECULES - GAUSSIAN-2 THEORY WITH BOND SEPARATION ENERGIES

Gaussian-2 (G2) theory is combined with isodesmic bond separation reac tion energies to yield accurate thermochemistry for larger molecules. For a test set of 40 Molecules composed of H, C, O, and N, our method yields enthalpies of formation, Delta H-f(0)(298 K), with a mean absol ute deviation from experiment of only 0.5 kcal/mol. This is an improve ment of a factor of three over the deviation of 1.5 kcal/mol seen in s tandard G2 theory. (C) 1997 American Institute of Physics.