Density-functional thermochemistry. I. The effect of the exchange-only gradient correction

Previous work by the author on diatomic molecules and by others on polyatomic systems has revealed that Kohn–Sham density-functional theory with ‘‘gradient corrected’’ exchange-correlation approximations gives remarkably good molecular bond and atomization energies. In the present communication, we report the results of an extensive survey of density-functional atomization energies on the 55 molecules of the Gaussian-1 thermochemical data base of Pople and co-workers [J. Chem. Phys. 90, 5622 (1989); 93, 2537 (1990)]. These calculations have been performed by the fully numerical molecules (NUMOL) program of Becke and Dickson [J. Chem. Phys. 92, 3610 (1990)] and are therefore free of basis-set uncertainties. We find an average absolute error in the total atomization energies of our 55 test molecules of 3.7 kcal/mol, compared to 1.6 kcal/mol for the Gaussian-1 procedure and 1.2 kcal/mol for Gaussian-2.