CCL:G: triplet TDDFT calculation

Dear colleagues,
This is an answer to Michael Morgan.
I have used with success a somewhat rough and clumsy method for limiting spin contamination in excited states.
You will find it in:
P. Archirel et al. J. Phys. Chem. B 2015, 119, 5282−5298
I hope this will help,
Best wishes,
Pierre Archirel, LCP, Universite Paris-Sud, Orsay France

Dear All,


Standard TDDFT calculations calculate singlet->singlet excitations. In Gaussian, I can see that for each excitation, <S**2>=0.000.


While I calculate molecules like O2 which the ground state is triplet, I need calculate triplet->triplet excitations by assigning TD=triplet .
In output, I found all kinds of <S**2> values (from 2 to 4). I am confused: for those are not close to 3, are they still spin-allowed therefore
experimentally observable? Should I include them if I want to predict an absorption spectrum for the molecule?


Thank you very much!



  Pierre Archirel
  Groupe Théosim: Théorie et Simulation
  Laboratoire de Chimie Physique      Tel: 01 69 15 63 86
  Bât 349                             Fax: 01 69 15 61 88
  91405 Orsay Cédex
  France                   pierre.archirel/./