Calculated VDE from the
difference in energy between the reduced
form and a Franck–Condon transition (black) and from the −εHOMO (blue) for [Cu(NCS)2]1– (triangle), [Cu(SCH3)2]1– (square), FeCl4– (circle),
and [Fe(SCH3)4]1– (diamond),
using the DZVP2 basis set for hybrid functionals in order of increasing
(short-range) HF exchange. From left to right, the functionals (open
symbols) are B3LYP*, B97, B3LYP, PBE1PBE, M06, and B(38HF)P86. The
symbols are connected by dotted lines to guide the eye, and the results
for the Fe complexes are shifted upward by 3 eV to avoid overlaps.
The experimental PES values (gray line with error indicated approximately
by width of line) are also shown.