An extension of koopmans' theorem III. ionization energies of the open‐shell atoms Li and B

Extended Koopmans' theorem orbital energies are calculated using unsymmetrized hole states for the Li 2S and B 2P states. These orbital energies are compared with ionization energies obtained from Δci calculations in the same basis sets as well as with experimental ionization energies. The extended Koopmans' orbital energies over unsymmetrized hole states for the outer shell orbital 2sα of Li and for the two outer shell orbitals 2pα and 2sβ of B agree well with Δci ionization energies and with experimental ionization energies. The overlap of the 2sα hole state of Li with a ci wave function of Li+ is 0.999983. The corresponding overlaps of the 2pα and 2sβ hole states of B with ci wave functions are 0.996588 and 0.999258, respectively. The unsymmetrized hole states for inner shell orbitals are strong mixtures of different symmetry types and yield increasingly poorer ionization energies.