Optimized density functionals from the extended G2 test set

A recently suggested procedure for the systematic optimization of gradient-corrected exchange-correlation functionals [A. D. Becke, J. Chem. Phys. 107, 8554 (1997)] has been applied to the extended G2 test set [L. A. Curtiss et al., J. Chem. Phys. 106, 1063 (1997)], which consists of the standard heats of formation of 148 molecules. The limit of reproduction of the experimental data in this test set is found to be 1.78 kcal/mol mean absolute error, with a maximum of 8.89 kcal/mol error for the ozone molecule. This compares rather well with previous results for G2 theory itself (1.58 and 8.2 kcal/mol, respectively). We show that fair stability can be obtained by our optimization procedure.