respectively, localized on oxygen. Past 2.1 Å with the H core guess and 2.0 Å with
the Hückel guess, PBE0 is also unable to converge to any state. The Hückel guess
once again lands in an excited state at 1.7 Å that is 86 kcal mol
−1 above the ground
state. The ground state is a
5 A 1 and the excited state found at 1.7 Å is a
5 A 2 state.
The ground
5 A 1 state is a combination of an A 2 orbital, an A 1 orbital, a B 1 orbital,
and a B 2 orbital, all of which are d orbitals on iron. The excited state
5 A 2 results
from the occupation of two A 1 orbitals, a B 2 orbital, and a B 1 orbital, similar to the
population of the excited state calculated with B3LYP.
Fig. 18 Points calculated for FeO at the M06 level of theory, using the H core initial guess. The
calculations do not converge past 2.2 Å using the H core guess. Only four points on the curve
converged using the Hückel guess
Fig. 19 Points calculated for FeO at the M1 level of theory, using the H core and Hückel initial
guesses
24
R. Weber et al.