Comparison of second‐order orbital‐dependent DFT correlation functionals

The choice of the orbital‐dependent second‐order correlation functional plays the prime role in the description of the correlation effects in orbital‐dependent DFT calculations. Using second‐order perturbation theory we were able to derive the simplest orbital‐dependent correlation functional, but even at this lowest correlation level, we had several possibilities to define it. Applications of different second‐order correlation functionals for the atomic as well as molecular systems are presented. The ab initio DFT‐type OEP2 functionals based on Møller‐Plesset or semicanonical partitioning (OEP2‐sc) are compared with those based on Epstein‐Nesbet type partitioning, showing that the latter ones can fail in more difficult molecular problems, e.g., the Be dimer potential curve. We show that currently the best performing orbital‐dependent second‐order correlation functional is the OEP2‐sc one.