On the optimal value of α for the Hartree–Fock–Slater method

We have examined the performance of the analytic Hartree–Fock–Slater (HFS) method for various α values and empirically determined the optimal α value by minimizing the mean absolute error (MAE) in atomization energies of the G2 set of molecules. At the optimal α the HFS method’s performance is far superior with the MAE of 14 kcal/mol than that of the local density approximation (MAE ∼ 36 kcal/mol) and the Hartree–Fock theory (MAE ∼ 78 kcal/mol). The HFS exchange functional with α = 0.7091 performs significantly better than the Kohn–Sham exchange functional for equally weighted atoms H–Kr.