Hello,
I am a novice in quantum calculation.My system of interest is substituted Indole. From literature it is known that there are various excited electronic states like La Lb Ba Bb etc.I want to determine which among them is the most stable excited state for my system or is there any coupling or not.I have done the TD-DFT calculation. Please provide me the detail procedure.
Thanks
Hi
Dear Tonima Nandy
It is imperative to preoptimize any geometry using semi-empirical methods
(PM3 etc before submitting to ab initio calculations. In cases where PM3 arrives at
unreasonable minima, it may be useful to submit directly to ab initio calculations.
The easiest way to set up calculations in Gaussian is with the aid of the graphical
user interface (GUI) WebMO. The cartesian file generated in MOPAC, Gaussview
or any other text editing program can be uploaded into WebMO. Details on
using WebMO are not described here as they are described in the WebMO
manual:
http://www.webmo.net/download/WebMO_Users_Guide.pdf
sincerly
Dr. Pakizeh
How have you done TD-DFT calculations? I believe you should specify more than one excited state and then optimize the lowest one. This can be done 1) by using the keyword td=states=10 (for getting the lowest ten ES's). Then, 2) you may carry out a further calculation including opt td=(nstates=10, root=1).
Dear Tonima Nandy
I know it is unpleasant to have a very concise question and get a very broad answer... But here it is: Having long experience with the order of La and Lb state in indole(s), I must conclude that there are better solutions to this problem than using DFT based methods in Gaussian. TD-DFT is by no way exact enough to get the correct order of excited states in indole(s). I would recommend coupled cluster second order approach like implemented in CC2 in turbomole. The real problem that you will encounter is, that the vertically lowest state might only be the second or higher state adiabatically. You have to have already a quite good idea about the geometry changes you expect for the different excited states. Here you will find some examples:
DOI: 10.1021/acs.jpca.6b12605
DOI: 10.1002/cphc.201600420
DOI: 10.1063/1.4773468
dx.doi.org/10.1021/jp3042523
DOI: 10.1039/c2cp41094j
Best regards, Michael
Dear Prof. Dr. Michael Schmitt
Thanks for your valuable recommendation. I have been following your paper since a long time. As per your opinion I have tried to do it using Turbomole but reading the manual its not very clear to me the format of input control file. Can you give me the input file of any indole molecule?
Dear Tonima Nandy,
Sorry, I'm not often here, so I missed you question. In case that you are still interested here is my answer:
Turbomole is indeed a program that is easier to learn by guidance than through the manual, which is very useful, once you know, what you are doing.
There is no single "input file" as in Gaussian e.g. You need a file which defines the geometry (coord) and one which gives the options that you want to have (control). Additionally you need files for the basis set that you have chosen (basis), axiliary basis sets (auxbasis), the molecular orbitals (mos). The only thing you really need from the very beginning is the coord file with the geometry. Be carful, it is in Bohr units (not Angstrom). All other files are generated running define (a programme that is contained in Turbomole). I attach the coord and define for a ground state CC2 calculation with the cc-pVTZ basis.
A good starting point to learn how Turbomole works is NOT the manual but the tutorial, which gives a step-by-step instruction.
Best, Michael
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