# Singlet excited state optimization gaussian issue

I hope someone here can help me with some TD-DFT calculations. I am trying to calculate the excited state optimised structures and energies of some Germanium compounds. Firstly, I run a TD calculation of the first 10 excited states, singlets and triplets, using TDA=(Nstates=10,50-50) WB97XD/genecp

From this output, I see the first few excited state energies and they look ok to me:

Excited State   1:      Triplet-A
2.4156 eV  513.26 nm  f=0.0000
<S**2>=2.000
113 ->120        -0.18260
119 ->120         0.65189

This state for optimization and/or second-order correction.
Total Energy, E(CIS/TDA) =  -1629.19629051
Copying the excited state density for this state as the 1-particle RhoCI density.

Excited State   2:      Singlet-A
3.3296 eV  372.37 nm  f=0.0537
<S**2>=0.000
113 ->120        -0.18586
119 ->120         0.66543


I then try to optimise the first singlet and triplet as I want to see how the spin density looks like in those species. For the first triplet, I just indicate multiplicity 3 in the gaussian input (0 3 right before the coordinates), and I get something that I think makes sense; the molecule geometry changes and I get alpha and beta orbitals, one electron seems to be occupying a virtual orbital by itself.... etc

The problem comes with the first singlet excited state. In order to calculate it I use TD=(Nstates=6,50-50,root=2) WB97XD/genecp, based on the previous excited states calculation, in which the second state is the first singlet. However, after the calculation was done (it took quite a long time) I see an output with completely normal orbitals (not alpha and beta), a nice HOMO with two electrons and a empty LUMO, as in the molecule looks like a normal diamagnetic ground state molecule.

Does someone see something weird in my procedures? If you need any more details please let me know. My apologies if I am making some very basic mistakes I am very new in TD-DFT. Thank you all in advance!

## 1 Answer

If you want the excited singlet state, I suggest you only calculate these, and not the 50:50. Optimization with roots higher than 1 is often tricky, and if you only calculate the singlet excited states, then you have root=1. With that said, the orbitals you get are from the ground state. To get the excited state, use density=current. You can also use the NTO to get a condensed picture of the excitation itself.