The effect of different density functional methods on basis set parameters

It is shown that for density functional calculations, the use of basis sets optimized by density functional methods gives a small, but significant, improvement over basis sets optimized at the Hartree–Fock (HF) level. The difference between different exchange-correlation functionals, however, is very marginal, and significantly less than the inherent error relative to the basis set limit. The difference between methods diminishes as the basis set becomes larger, and the main variation is due to the contraction coefficients, and not the exponent values. The uncontracted forms of the previously proposed polarization consistent basis sets should thus be useful for establishing the basis set limit for any density functional method, as well as estimating the HF limit for molecular systems.