Communication: Simple self-correlation corrections to the Ragot-Cortona model of local correlation energy

The Ragot-Cortona or RC model of local correlation energy [J. Chem. Phys. 121, 7671 (2004)] improves the standard local approximation in various respects. This letter aims at illustrating the origin of this improvement. To that aim, simple self-interaction corrected versions of the RC model are implemented, which involve local energy differences only. Several correlation functionals are selected for direct comparison using Hartree-Fock charge densities of atomic ions (H(-) to Ar). One of the self-interaction corrected versions of the RC model shows surprising improvements over the initial RC model. First, it dramatically improves the atomic correlation energies of atomic ions. Second, the impact on the contribution of the correlation energy to ionization potentials or electron affinities is still more convincing. In both cases, the accuracy achieved is close to or better than a selection of gradient-level functionals.