ASSESSMENT OF BASIS-SET AND FUNCTIONAL-DEPENDENCIES IN DENSITY-FUNCTIONAL THEORY - STUDIES OF ATOMIZATION AND REACTION ENERGIES

In search of the optimal combination of basis set and exchange-correla tion potential, we have investigated the dependence of the atomization energies (D-0) and reaction enthalpies (Delta H) for a set of 44 mole cules using gradient-corrected density functional theory. Of the Six f unctionals tested, those that include a portion of the exact (Hartree- Fock) exchange perform best and yield D-0 values that generally lie wi thin 3-5 kcal/mol of the experimental value. For the functionals in wh ich pure DFT exchange is employed, the errors in D-0 are instead on th e order of 8-10 kcal/mol. Conversely, reaction enthalpies show slightl y better agreement with experimental results when pure DFT exchange is employed. For both D-0 and Delta H the four Gaussian basis sets 6-31G (d,p), 6-311G(d,p), cc-pVDZ, and cc-pVTZ show similar behavior. The mo st accurate predictions were obtained using the largest cc-pVTZ basis. There is a significant variation in these energies obtained with the various functionals depending on the basis set employed.