I am trying to understand how to interpret the TDDFT results ( I know there is another post for this but it does not answer my question ). Here is part of the result from GAMESS:


I downloaded Chemissian and this is its result for this state:

Chemissian Output

I have two related questions:

1-How did it calculate this 1.41 from the amplitude of this state ?
2-Does it have anything to do with λmax ?

  • $\begingroup$ Which reaction are you talking about? The question is vague. Energy can be transferred through collisions even in liquids. And such collisions can lead to emission of electrons. The Helium-Neon laser operates like this en.wikipedia.org/wiki/Helium%E2%80%93neon_laser $\endgroup$ Commented May 9, 2015 at 1:40
  • $\begingroup$ that should just be the transitions of the orbitals and your $\lambda_\mathrm{max}$ should be somewhere around $9.3~\mathrm{eV}$ judging from the spectrum. Note that the state you have selected has 0.000 oscillator strength. $\endgroup$ Commented May 12, 2015 at 8:30
  • $\begingroup$ @Martin-マーチン this is the output for Acetone and related to my other question about Acetone behavior. I am confused what is going wrong and how this 1.41 is calculated $\endgroup$
    – Aug
    Commented May 12, 2015 at 13:35
  • 1
    $\begingroup$ These are terrible tags! Reaction mechanism? Heat? Transition state theory? They don't make any sense. $\endgroup$
    – Greg
    Commented May 15, 2015 at 11:06

1 Answer 1


You are looking at the wrong numbers.

You should look for excitation that has non-zero oscillator strength. In the text file "State # 1,2 .." and in Chemissian on the left, list with columns "# Energy Strength" The transitions with zero or very small oscillator strength has a very low intensity in the spectrum, so you don't see them. In your case the relevant excitation are #2 (Energy: 6.691 eV, Strength: 0.027) and #4 (Energy: 8.353 eV, Strength: 0.042), and you can see them as small peaks on the graph down.

The "amplitude .. 1.41" has nothing to do with the oscillator strength. It tells you which orbital contributions are the most important ones for the given excitation.


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