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Re^9: Can't figure out how to find emission spectra of Benzene...

Siddheshwar Chopra

Dear Pavlo,
Thank you for your motivation and I have finally started obtaining the emission spectra of samples. I need to know few things here. I find spectra with NSTATE=10-100. I obtain absorption and emission spectra both.. But I just need to know what about HOMO-LUMO gaps obtained from both the abs. and emission calculations? Are these the gaps between (S1* <-- S0)(for abs.) and (S1 --> S0)(for emission), which are easily obtained using Gausssum? So do we mean that the sample EMITS a single wavelength photons with energy given by (S1 --> S0) gap OR DO we discuss the emission spectra which is some intensity emitted at every wavelength, say 100-900nm?

The doubt is whether I discuss a single transition (S1 --> S0) or complete spectra? Also how do we get the (S1 --> S0)gap value from the spectra?


On Tue Jun 24 '14 4:49pm, Pavlo Solntsev wrote
>Sorry, but did you read my first post? As i said, Gradient/TDDFT+PCM is not yet implemented. Solvent can affect an excited state geometry. Therefore, it is better to have some experimental information, such as solvent dependency for UV-vis and Luminescence. It may help you to judge a solvent effect. There are other methods available where you can consider a solvent correction for excited state optimization, i.e. MCSCF. I would recommend you to do a literature search. Try to learn more about the system of interest. You should get a plan of your theoretical work before you create an input file. IF you miss something go back and try to fix this by reading articles, text-books etc. But you should get clear understanding what you are trying to do and why.

>Good luck.
>On Tue Jun 24 '14 8:21am, Siddheshwar Chopra wrote
>>Dear Pavlo,
>>There is one more observation which came across to me from your files.. I noticed that you considered solvent CH2Cl2 in your study. You have NOT considered solvent effect while optimizing the S0* and S1* levels. However you have included it while performing TDDFT calculations for absorption and emission. Shouldn't we optimize the sample throughout in the presence of solvent too? There will be some exchange of electrons for sure.

>>Please help me understand this.

>>Kind Regards,

>>On Fri Jun 20 '14 2:42pm, Pavlo Solntsev wrote
>>>On Fri Jun 20 '14 1:01pm, Siddheshwar Chopra wrote
>>>>Dear Pavlo,
>>>>Thanks for the useful answers. I have some points:
>>>>1) I will then keep the state tracking on always. however I dont know how to track this flipping of states manually. I came to know of tdprp=.t., to get excited state properties. Is it good to try??

>>>There is no option to track a state manually, AFAIK. About TDPRP, it is always good to try.
>>>>2) Regarding B3U.. i used gausssum... with no symmetry constraint...
>>>gausssum is basically a wrap for cclib. It reads information from you output file. In you output file your molecule has C2 symmetry.

>>>>3) Thanks for the
>>>>4) regarding mcscf one... Pavlo I am actually interested in fluorescence only... so I think state tracking won't be essential in my case.. what do u say?

>>>It is important for geometry optimization of an excited state. Different systems, different situation. I know system where you have to optimize state #17 to get luminescence.

>>>>5) One most important question to u: Is it the same way I should check for imaginary frequencies for the S1* state, like we do for S0?? I must run hessian for every optimization right?

>>>Technically- yes.

>>>>kind Regards,

>>>>On Tue Jun 17 '14 2:58pm, Pavlo Solntsev wrote
>>>>>On Tue Jun 17 '14 1:25pm, Siddheshwar Chopra wrote
>>>>>>Dear Pavlo,
>>>>>>I really appreciate all your help. Your guidance has helped me a lot always.
>>>>>>Sir, regarding you replies:
>>>>>>1) regarding state tracking... do you mean to say if i m studying singlet to singlet transition, then it is not necessary??
>>>>>No.It just help you to track (watch) the state of interest if order of states changes during the geometry optimization. I believe the optimization of triplet state should be the same as singlet.

>>>>>>In general can I take it as a rule of thumb to switch it on always?? Like you did..
>>>>>>I just need to add - sign to activate it..and then i dont need to bother about anything else right??
>>>>>It is make sense for geometry optimization only. Yes, it is safe to leave it on.

>>>>>>2) I understood about using optimized coords. Of S0 for S1*.. thnx for that..
>>>>>>But how did you know B3U is first excited state? I checked my o/p file with gausssum.I couldn't get that information.. i could only find A and B..
>>>>>What is the point group of porphyrin? Gaussian used C2 group. It is problem with Gaussian.

>>>>>>3) Regarding PCM... i checked 8.0.x manual.. but couldnt find the list of solvents.. :-(

>>>>>>4) Pardon me about the last one... I am unsure about it as I read in this forum that active space is created.. yes it is not is MCSCF/XMCQDPT2...
>>>>>>I just wish that the procedure you have told me will be the best suited for my needs.. :-)
>>>>>>Pavlo following the same procedure, I can get singlet to either singlet or triplet transitions/emission spectra..right? But then for downward transitions, the gnd state multiplicity will change..
>>>>>Probably it is correct to talk about phosphorescence. If you optimized triplet state and then looking for transition to a singlet.


>>>>>>Kind Regards,
>>>>>>On Mon Jun 16 '14 9:18pm, Pavlo Solntsev wrote
>>>>>>>On Mon Jun 16 '14 11:00am, Siddheshwar Chopra wrote
>>>>>>>>Dear Pavlo,
>>>>>>>>Sorry for replying late. I just went through all the files you had provided. I am really grateful to you for taking out time to make us understand this so well. I am really thankful to you.
>>>>>>>>Pavlo I checked all the files and would be glad if you could answer some basic questions:

>>>>>>>>1) The emission spectra is obtained from the file "pp_opt_s1_tddft.out"?

>>>>>>>>2) From S1*--> S1... How to use and understand state tracking? I actually don't understand what I am supposed to do with it. I just know how to turn it on. What happens if I switch it off?

>>>>>>>In example i gave you, state tracking probably doesn't matter. However, if you want to relax say state #3 then it may be swapped with other state. In that case state tracking should be turned on. See $TDDFT ISTATE $END description.

>>>>>>>>3) You said "1st excited state is B3U"...and used the same optimized coordinates of S0 while optimizing the S1*. Is it right?
>>>>>>>Of course it better to start from good coordinates for excited state optimization. The best chose is ground state geometry.

>>>>>>>> What should I do with the "1st excited state is B3U"?
>>>>>>>Nothing. It is just first excited state of porphyrin.

>>>>>>>>This step is very important for understanding. By using the optimized coords. of S0 in optimizing S1*, do you mean that the coordinates of atoms don't change in excited state?
>>>>>>>No. Any geometry optimization by definition changes atomic coordinates.

>>>>>>>>4) You have used PCM calculations all throughout.. They don't seem time consuming. What all solvents I could use for the same? Do I have acetonitrile available?

>>>>>>>Did you check manual? There are two manual available. Th new one and old. Check both of them. CH3CN is available.
>>>>>>>>Pavlo until your help, I was in this notion that I should get the most probable orbitals from UV-Vis. calculations and then optimize them for S1 and then obtain the emission spectra. But you haven't talked about most probable orbitals anywhere... Where do I apply the concept I just mentioned then?

>>>>>>>Sorry, by i don't understand what you are trying to say within DFT level of theory.
>>>>>>>Hope this helps.

>>>>>>>>Kind Regards,
>>>>>>>>On Thu Jun 12 '14 10:18am, Siddheshwar Chopra wrote
>>>>>>>>>Dear Pavel,
>>>>>>>>>Your suggestions have always been valuable to me. I will start working on your files and will let you know in case I need your help.

>>>>>>>>>Kind Regards,

>>>>>>>>>On Wed Jun 11 '14 4:17pm, Pavlo Solntsev wrote
>>>>>>>>>>I attached example how to do Luminescence calculation for porphyrin molecule. For more detailed information please, check manual AND this forum.

>>>>>>>>>>Salvation model has not been programmed for TDDFT+gradient. Therefore, optimization of the excited state was done without solvent correction. However, this correction was included into spectra calculation.

>>>>>>>>>>Very often geometry optimization of the excited state brakes a true molecular symmetry. Keep this in mind.

>>>>>>>>>>For more complex systems state of interest may be different, not S1. It is especially true if you have a donor group in your molecule and thus HOMO....HOMO-x belong to the donor, but you are looking for emission within porphyrin core. In such case you need identify the state of interest based on TDDFT(ground state) and knowledge.

>>>>>>>>>>Good luck.

>>>>>>>>>>On Tue Jun 10 '14 10:16pm, Siddheshwar Chopra wrote
>>>>>>>>>>>Dear Alex,
>>>>>>>>>>>I searched a lot on this forum regarding the same. What you told is right and I know these too. But I want to step by step how to optimize �the S1? say for �benzene.
>>>>>>>>>>>And then how should I determine S0--> S1 (optimized)?
>>>>>>>>>>>Please help me stepwise. Any i/p files would be of great help.. I have noted from TDDFT calc of benzene that orbitals 17-24 are most dominant ones. How do I proceed next?

>>>>>>>>>>>Kind Regards,

>>>>>>>>>>>n Tue Jun 10 '14 7:43pm, Alex Granovsky wrote

>>>>>>>>>>>>for emission spectra you need to optimize S1 geometry and then compute
>>>>>>>>>>>>vertical transition from S0 to S1 at optimized geometry of S1.

>>>>>>>>>>>>Kind regards,
>>>>>>>>>>>>Alex Granovsky
>>>>>>>>>>>>On Sat Jun 7 '14 9:10pm, Siddheshwar Chopra wrote
>>>>>>>>>>>>>Dear Firefly users,
>>>>>>>>>>>>>I need some real help in determining the emission spectra (S1--->SO*) of benzene.
>>>>>>>>>>>>>I have understood till optimizing the ground state and then obtaining the vertical transition from SO--->S1*...
>>>>>>>>>>>>>Please help me now what I should do next? Any i/p files would be welcomed.

>>>>>>>>>>>>>Kind Regards,

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