The importance of diffuse f functions for transition metals

The importance of a diffuse f function for determining the dissociation energy (De) of Cu2 and the 3F–3D energy separation in Ni atom is investigated. It is found that the diffuse f contributes at most 0.05 eV to the De of Cu2 when added to a basis containing tight f functions and a flexibly contracted d basis. The diffuse f function is found to decrease the 3F–3D separation in Ni, but by substantially less than the tight f functions.