Accurate atomic electron affinities calculated by using anionic Gaussian basis sets

The computation of accurate electron affinity (EA) remains one of the most difficult tasks in quantum chemistry. A major source of error in EA calculations is the inadequacy of the basis set (BS) to represent the anionic system, since the Gaussian exponents are normally optimized for the neutral atom energy. To overcome this problem, one must augment the BSs with diffuse functions, which allow a better description of long-range interactions in anionic systems. Here, we report a new methodology to generate BSs for accurate EA computation that consists in the direct optimization of the Gaussian exponents in an anionic environment. By using the anionic basis sets (ABSs), we substantially reduce the errors in EA calculation for boron, carbon, oxygen and fluorine. A graphical analysis of the ABS parameters shows that their exponents are able to span important regions for short- and long-ranged interactions, which permit the ABSs to properly describe both neutral and anionic systems.