DENSITY FUNCTIONALS FROM THE EXTENDED G2 TEST SET - 2ND-ORDER GRADIENT CORRECTIONS

In a recent paper [H. L. Schmider and A. D. Becke, J. Chem. Phys. 108, 9624 (1998)], we applied a systematic method for the determination of exchange-correlation functionals within the generalized gradient appr oximation (GGA) to the extended G2 test set of standard heats of forma tion of Curtiss et al. [J. Chem. Phys. 106, 1063 (1997)]. In the prese nt work, we apply a similar methodology that goes beyond the GGA by ta king second-order gradients and the (noninteracting) kinetic-energy de nsity into account. The resulting improvement in the reproduction of t hermochemical data brings us very close to the quality of G2 theory it self. Our lowest mean absolute error for standard heats of formation, 1.60 kcal/mol, is only marginally greater than the G2 value (1.58 kcal /mol). The corresponding largest deviation is 9.97 kcal/mol, as compar ed to 8.2 kcal/mol for G2 theory. (C) 1998 American Institute of Physi cs. [S0021-9606(98)30343-8].