Exact exchange treatment for molecules in finite-basis-set Kohn-Sham theory

The exact orbital-dependent exchange (EXX) energy formalism within the line ar-combination-of-atomic-orbital Kohn-Sham density functional theory for po lyatomic molecules is presented and implemented. The exchange energies and occupied orbital; energies obtained from EXX are very close to the correspo nding Hartree-Fock (HF) values, whereas the EXX unoccupied orbital energies are significantly lower than the HF values. We demonstrate that the curren t approximate correlation functionals deteriorate the orbital energies when combined with EXX.