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Re^7: Problem with Hessian and TDDFT calculations..

Thomas Pijper

Dear Siddheshwar,

Could you please post the output? That will allow me to see what is wrong with it.

As to ISTATE and NSTATE, please have a close look at the description of these keywords in the manual (the file Firefly_input_rev002.pdf has them). ISTATE selects a state of interest, not the multiplicity of the states considered (the MULT keyword does this). NSTATE selects the number of states that should be calculated. It is important to understand that TDDFT is not a UV/vis spectrum simulation tool. TDDFT can be used to obtain information on electronic excited states (energies and transition dipole moments / oscillator strengths). NSTATE=1 request the TDDFT program to consider only the first (lowest) excited state, NSTATE=2 the first and second (the two lowest) excited states, etc.

It just happens to be that UV/vis spec. also provides this information. The absorption band with the longest wavelength most likely corresponds to your first excited state. The one next to it most likely corresponds to your second excited state. Etc. Note that I say "most likely", because electronic states with a very small transition dipole moment do not show up in your UV/vis spectrum (but are considered in TDDFT). Also, states that lie close in energy typically show up as one band (UV/vis spectroscopy at room temperature has a poor resolution).

I hope it is clear that this means that you cannot use the TDDFT program to calculate all states in a given wavelength range -- the program has no way of knowing which states have which energies (= wavelengths) until after the calculation is complete. So, it is up to the user to request enough states. IIRC, for a polyaromatic molecule you may need NSTATE=30 or higher to get information about states up till 220 nm.

Kind regards,

On Tue Mar 4 '14 2:09pm, Siddheshwar Chopra wrote
>Dear Sir,
>I admit that DATA group has many errors. I rectified them. But still the problem persists.. COuld you point out the errors in details?
>Also I need help from you in understanding $TDDFT command. I understand that ISTATE =1 or 3 (singlet and triplet),ISTSYM and TDA=.t.
>But I not understand NSTATE.. How do i set its value?? I just know that I need the UV absorption spectra from 200-900 nm excitation range. How should I set this parameter?? I just want more number of data points to get a smooth curve.. Does NSTATE mean number of times the oscillator strength/intensity will be calculated for every 1nm of x-axis???
>The program runs successfully but doesnt open with Gausssum... And it finished in seconds..Thats very strange. What wrong am I doing?

>On Tue Mar 4 '14 1:45pm, Thomas Pijper wrote
>>Dear Siddheshwar,

>>Please check your input file, specifically the $DATA group. It contains multiple errors.

>>As to your question regarding optol 10-8 and NCONV=8, recall that the $STATPT group and its keywords (incl. OPTTOL) control the parameters for a geometry optimization. As to NCONV in $SCF, this controls the tightness of the SCF procedure.
>>Kind regards,
>>On Tue Mar 4 '14 12:48pm, Siddheshwar Chopra wrote
>>>Dear Sir,
>>>Your point taken perfectly. I will do as you directed. optol 10-8 and NCONV=8, what is the difference between these two?
>>>Regarding TDDFT, I would be grateful if you could run the i/p file I sent you... I perhaps copied the wrong coordinates which resulted in the error. But when I added the correct coordinates, I ran the checkrun. It completed in seconds.. But again when I ran the same program properly, it completed in seconds.. And with NSTATE=100 and more. I dont know how it happened and the o/p file does't open with Gaussum. It gives some cclib parsing error. There is no calculation done at all and the o/p says...Program terminated normally. Please help. I cannot figure it out.


>>>On Tue Mar 4 '14 11:41am, Thomas Pijper wrote
>>>>Dear Siddheshwar,

>>>>A few comments:

>>>>$SCF NCONV=8 is very tight, I'd say that the default NCONV=5 would be sufficient in your case.

>>>>$TDDFT NSTATE=100 is a lot of states. I expect that 30 to 40 states is enough if you are trying to obtain a UV/vis spectrum. This should speed up your calculation significantly.

>>>>$CONTRL INTTYP=HONDO ICUT=11 ITOL=30 should not be necessary (unless you are calculating a numerical gradient). Same goes for $DFT LMAX=41 NRAD=99. This will help in speeding up your calculation.

>>>>$BASIS GBASIS=N31 NGAUSS=6 is a very light basis set. I would at least try to add NDFUNC=1 (resulting in the 6-31G(d) basis).
>>>>Kind regards,
>>>>On Tue Mar 4 '14 10:07am, Siddheshwar Chopra wrote
>>>>>Dear Sir,
>>>>>Thank you for pointing out this silly mistake of mine. I will note this down now. As for the TDDFT calculations please find attached the i/p file. I have used the lowest energy state coordinates for the same. Please have a look at it.


>>>>>On Mon Mar 3 '14 5:51pm, Thomas Pijper wrote
>>>>>>Dear Siddheshwar,

>>>>>>> I ran HEssian calculations on my sample first. I
>>>>>>> got NO imaginary frequencies. But I could not find
>>>>>>> "Equilibrium geometry located" text anywhere.

>>>>>>This is because you specified RUNTYP=HESSIAN. This performs a Hessian calculation. The message "Equilibrium geometry located" appears only with a completed geometry optimization (RUNTYP=OPTIMIZE or SADPOINT). Your geometry does correspond to a minimum on the PES.
>>>>>>> I run TDDFT calcs. But in that I am getting this error now:
>>>>>>> * ... LESS THAN �3.000
>>>>>>> **** THERE ARE ATOMS LESS THAN � 0.100 APART, QUITTING... ****
>>>>>>Most likely you made an error in the $DATA group of the TDDFT calculation input. It could for example be that you specified a point group other than C1, but specified coordinates corresponding to the C1 geometry, thus causing some atoms to be specified twice. If you would like me to take a closer look at the problem, feel free to post the input file for your TDDFT calculation.
>>>>>>Kind regards,
>>>>>>On Mon Mar 3 '14 11:21am, Siddheshwar Chopra wrote
>>>>>>>Dear Sir,
>>>>>>>I ran HEssian calculations on my sample first. I got NO imaginary frequencies. But I could not find "Equilibrium geometry located" text anywhere. Now thinking that it is a global minimum, I run TDDFT calcs. But in that I am getting this error now:

>>>>>>> �* ... LESS THAN �3.000

>>>>>>> **** THERE ARE ATOMS LESS THAN � 0.100 APART, QUITTING... ****

>>>>>>>What is wrong here? What should I do next to rectify this. If the sample was not in global minima, then how come there were no imaginary freqs?


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