Just check 1) the total electronic energy and 2) the C–H distances and you’ll know if the geometry optimization converged to the GS. As for the electron occupancy, please consider that GaussView will always apply the auf-bau rule.

If you are interested in a deeper understanding of ES calculation, please refer to a very recent paper we have published dealing with the absorption/emission properties of a bifluorene compound:

https://pubs.rsc.org/en/Content/ArticleLanding/2023/CE/D2CE01552H

For something easier, I recommend repeating the calculations on formaldehyde and benzene reported here:

https://www.sciencedirect.com/science/article/abs/pii/S0009261406001254?via%3Dihub

You can use these compounds as reliable examples for your tests.

Thank you very much for the detailed answer, professor Arca.

Now I totally understood how to interpret the result I received.

I ran an optimization job of benzene in S1 state using

#p opt td pbe1pbe/6-31G

and was able to reproduce the result mentioned in:

https://www.sciencedirect.com/science/article/abs/pii/S0009261406001254?via%3Dihub

Also, from the S11 of your publication,:

https://www.sciencedirect.com/science/article/abs/pii/S0009261406001254?via%3Dihub

I figured that in many cases, one excited state’s electronic configuration cannot be simply assigned by one transition (e.g. only HOMO→LUMO) but there are multiple contributions from various transitions (e.g. HOMO→LUMO and HOMO-1→LUMO+1).

Thank you again for your clear explanations.