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I am currently working with a system of 30 atoms of a organic molecule. I need to make a study related to determine the UV-Vis graphic as precisely as possible.

I am using DFT method. However, I am having trouble to find a methodology and basis set to obtain a proper result of the experiment.

Does anybody know what methodology and basis set I should use?

P.S: I have already tried B3LYP with 6-31G(d), 6-31G(d,p) and 6-311++G(2d, 2p) in sequence but the results weren't good.

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    $\begingroup$ Simple functionals and Pople-style basis sets are notoriously bad for UV/Vis. DFT and TD-DFT in general aren't that great, unfortunately, AFAIK, but there may be some decent options. I'll ping an expert in chat to come take a look. $\endgroup$
    – hBy2Py
    Commented Mar 7, 2018 at 12:34
  • $\begingroup$ Ooof. Said expert is in the middle of an international move, and not reachable in chat at the moment. $\endgroup$
    – hBy2Py
    Commented Mar 7, 2018 at 12:35
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    $\begingroup$ Look for benchmark papers from Denis Jacquemin. $\endgroup$ Commented Mar 8, 2018 at 12:14
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    $\begingroup$ I think you need to be more precise about "weren't good." There are many benchmarks, but results are generally accurate to ~0.2 eV. Are you including a solvent model, for example? $\endgroup$ Commented Mar 8, 2018 at 14:40
  • $\begingroup$ The other question is whether you're just trying to get low-lying $\pi-\pi^*$ transitions or you want CT or Rydberg states. $\endgroup$ Commented Mar 8, 2018 at 14:41

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