CCL:G: Experimental and theratical UV calculation



Dear Saurabh
Sure we can, we can compare theoretical calculations with the experimental one.
But you should be aware of some points, firstly, your structure should be the optimized one (I don't mean here after optimization, I mean your structure is the structure of the experimental one under solvation effect).
About, the number of states, it is depending on you experimental one, for example your experimental lamda max is around 280nm (for example) and your run your TD calculation based on 10 states and found the your excitation states didn't reached the desired one (i.e. 280nm) and stops at 300nm, so you should Add more states. So, there is no optimum number of states. You start with small number and then add more states until reach your desired wavelength.
Sure, solvation has a big big effect on your TD calculations and on all calculations in general. And here I would like to send a small experience in studying solvation effect, DON'T Trust always in solvation modeling, Some times you have to add explicit water molecules.
Through out the last of weeks I was doing theoretical UV Data for some complexes, so if you like me to have a look on your UV spectra (theoretical and expremental one), send it.
But, there is one keyword I couldn't understand its effect, it is called EqSolv. It says makes equilibrium solvation on your system using PCM model. But, it doesn't add solvation model and you need to add solvation model keyword in addition to Eqsolv.
I would like to push you forward and say you can get the same exactly UV spectra theoretical as the experimental one, but the problem is to mimic your system well.
Sincerely;
M. Ibrahim

Mahmoud A. A. Ibrahim

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--- On Mon, 5/25/09, Ismael Ortiz Verano ieortizv*bt.unal.edu.co <owner-chemistry:-:ccl.net> wrote:

From: Ismael Ortiz Verano ieortizv*bt.unal.edu.co <owner-chemistry:-:ccl.net>
Subject: CCL:G: Experimental and theratical UV calculation
To: "Ibrahim, Mahmoud A. A. " <m.ibrahim1982:-:yahoo.com>
Date: Monday, May 25, 2009, 11:35 AM

Saurabh

Perhaps 15 states are not sufficient, and in order to get accord with the experiment, you can calculate more states (try 40 or 50).

I think that when you compare your theoretical results, you obtain only wavelenghts of low energy (red).

If you are looking for a better accord, you can carry out a calculation that includes solvent's effect.

--
Ismael Ortiz
Grupo de Química Teórica
Universidad Nacional de Colombia
Tel: (57)(1) 3165000 ext 10608


2009/5/23 Saurabh Agrawal Saurabh.Agrawal!A!ucdconnect.ie <owner-chemistry*o*ccl.net>
Hello,

I have calculated UV absorption spectrum for some molecules using Gaussian. With the following basis set and cards.

#p B3LYP/6-31g** TD(Singlet,NSTATES=15) guess=read geom=check

The results I got are considerably different from experimental results.

1) Can we compare the theoretical results with experimental results? I appreciate if some one could send link for some basic notes on it.

Sincere regards,

Saurabh



Saurabh Agrawal,
PhD Student,
Department of Chemical and Bioprocess Engineering,
UCD, Belfield,
Dublin-4, Ireland



--
Ismael Ortiz Verano
Grupo de Química Teórica
Universidad Nacional de Colombia
Tel: (57)(1) 3165000 ext 10608