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I want to calculate the absorption spectra of molecules (and possibly ions) with TD-DFT.

I have used Gaussian in the past and, to my knowledge, the application of TD-DFT is implemented in this code. However, when looking at descriptions, particularly the results in GaussView, the spectra are reported as UV/Vis. Why is this? Shouldn't it be possible in principle to study a larger range of spectra?

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    $\begingroup$ I think that's because TD-DFT usually probes first or first few electronic excitations (number of roots requested) which have energy in the UV-vis range. You could request higher energy excitations in TD-DFT and get other types of spectra (in fact I believe X-ray absorption spectra can be calculated with TD-DFT) $\endgroup$
    – S R Maiti
    Mar 20 at 14:06
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    $\begingroup$ If you calculate the vibrational frequencies (Hessian), Gaussview should give you an IR spectra $\endgroup$
    – S R Maiti
    Mar 20 at 14:07
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    $\begingroup$ @SRMaiti x-ray absorption can indeed be computed with TD-DFT but it requires a different implementation since the core-excited roots would otherwise require computing thousands of excitations before you even get to the absorption edge! $\endgroup$
    – Susi Lehtola
    Mar 21 at 11:48
  • $\begingroup$ I gave my +1 long ago, but I wonder if there's any update you can give us after all these months? Also, are you still actively in need of an answer to this question? Were the comments by SR Maiti and Susi helpful? $\endgroup$
    – Nike Dattani
    Oct 12 at 15:36

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