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Re^9: Regarding the CITYP=TDDFT calculation for the excited state

Siddheshwar Chopra
sidhusai@gmail.com


Dear John McKelvey Sir,
Thanks for your views and guidance on the question asked. Sir with due respect I would like to add here that I have been an experimentalist for a long time, but really felt the need to be closer to the theory and also felt incompleteness in the explanation of exptl results.
Sir your views speak of the worthy experience you had with identifying or analyzing the absorption spectra. However, I have only one confusion regarding the computational research which I have started sometime back... What if we wish to study a system which has not been experimented with yet?? I mean we are actually artists... we imagine,draw and want to study this new system... I need to hear your views on this.
Yes truly said by you, pi-pi* seems to be the usual choice... But still there must a way to characterize these transitions.. I read that molar absorptivities differ a lot for various transitions.. will this help me somewhat Sir??
I am really happy to receive your motivation to continue this search.
You have reminded me again of " Curiosity is the mother of invention.." So stay curious.
Thank you again,

Kind Regards,

On Wed Sep 3 '14 7:46pm, Alex Granovsky wrote
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>On Wed Sep 3 '14 3:21pm, Siddheshwar Chopra wrote
>-------------------------------------------------
>>Dear Alex,
>>Ok. Could you tell me how should I check the symmetry type of the orbitals? Also how do I get the nature of the first excited state? I mean is 1A1, 1B2 etc. I just know about multipicity here Sir. Please hep me understand this. I actually want to be able to discuss the kind of transitions I obtained from the absorption spectra.

>>Kind Regards,

>Dear Siddheshwar,

>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.
>
>
>John McKelvey
>
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