Assigning Photoelectron Spectra of Transition Metal Organometallic Complexes on the Basis of Kohn−Sham Orbital Energies

Abstract

Kohn−Sham orbital energies may be interpreted as approximate vertical ionization potentials. A new method is proposed to correct the 2−3 eV difference in the measured and predicted vertical ionization potentials produced by standard DFT functionals and basis sets. Negatives of Kohn−Sham orbital energies are shifted so that the orbital energy of the HOMO matches the negative of the first vertical ionization energy obtained as a difference in the energy of the ground-state ion and ground-state neutral molecule at the equilibrium geometry of the latter. This way, photoelectron spectra can be predicted without prior experimental information. Standard DFT functionals (B3LYP, B3PW91, BLYP, B3P86) and basis sets (LanL2DZ, 6-311G**, TZVP) were utilized to probe this method for transition metal carbonyl complexes. At the B3LYP/TZVP level, the first vertical ionization energies were computed with an average difference of 0.00 ± 0.22 eV. A good accordance between the predicted and the experimental ionization energies was achieved, and the orderings of MOs were in line with the most reliable assignments available in the literature.