John McKelvey asked me to post the message below on behalf of himself.
(he has some problems to post on the forum directly)
With respect to the above post: During over 20 years of doing dye "Lmax" calculations I have had to respond to dye chemists' questions of how to map computed results onto experimental results. We found no definitive answers in the beginning other than assuming for dyes that transitions are from pi->pi* excitations which are readily identifiable in calculations.. Unless there is extremely high symmetry we typically compared the experimental extinction coefficients with observed absorption intensities. We found that for DFT results and and results from semiempirical methods such as Zerner's INDO/S this worked quite well. Doing these comparisons ultimately depends on comparing *relative* results between theory and experiment. For example theory can be extremely useful , and usually reliable, in mapping with experiment, even if the computed results were off 100nm! It takes a bit of time to learn how to stare at stick diagrams in comparison with spectra to have confidence in associations. This is probably not what one wishes, but over the decades at Kodak it worked!
Probably the most widespread application on MO method application in the world resulted from understanding how to use the Huckel method in designing the light sensitive materials in photographic film and paper, and was critical in designing black and white panchromatic film, and was transferable to color photography..
Hope this is helpful.