Orbitals from a self-interaction free Kohn–Sham potential as a single electron basis for ab initio methods

In the present work we study how well orbitals obtained from either an effective exact exchange Kohn–Sham approach or from a BLYP computation are suited as basis functions for ab initio approaches. These orbitals are compared with CASSCF and canonical Hartree–Fock orbitals. The usefulness of the various orbitals is discussed by means of the effort needed to push the error of a MR-CI computation below a given threshold. We consider as a test case the excited states of ethene and find that orbitals from the effective exact exchange Kohn–Sham approach perform very well.