We have examined the performance of the analytic Hartree-Fock-Slater (HFS) method for various a values and empirically determined the optimal a value by minimizing the mean absolute error (MAE) in atomization energies of the G2 set of molecules. At the optimal a the HFS method's performance is far superior with the MAE of 14 kcal/mol than that of the local density approximation (MAE similar to 36 kcal/mol) and the Hartree-Fock theory (MAE similar to 78 kcal/mol). The HFS exchange functional with alpha = 0.7091 performs significantly better than the Kohn-Sham exchange functional for equally weighted atoms H-Kr. (C) 2004 Elsevier B.V. All rights reserved.