Author Topic: 1st and 2nd triplet excitation using ESCF for a Platinum complex  (Read 6438 times)

mimonge

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I have tried an ESCF run on a Pt complex in order to analyze the two lowest triplet excitations. I am using B3LYP and SVP basis sets (as usual).
The results seem to be quite good regarding both the excitation energies and the composition of the frontier orbitals involved in the triplet transitions.
As expected we found an Intraligand transition and a MLCT one as observed experimentally. The only problem arises from the orbital labels since the 1st triplet excitation starts from orbital 164a (HOMO-1) and arrives to 166a (LUMO) meanwhile the 2nd triplet excitation starts from orbital 165a (HOMO) and arrives to 166a (LUMO) (it is the first time it happens to me)

My question is how can be explained that the HOMO-LUMO transition is not the lowest triplet excitation.

The first thing I have tried is a geometry optimization of both excited states in order to check if the energy of the 164a and 165a orbitals in S0 (ground states) change drastically in the T1 or T2 states.

Thanks in advance

Miguel

wwwups

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Re: 1st and 2nd triplet excitation using ESCF for a Platinum complex
« Reply #1 on: March 21, 2008, 05:21:36 AM »
I might be wrong, and this answer may be too late, but did you consider looking the orbitals to see if any of them were diffuse orbitals? CIS (or its TD-equivalent) usually uses HF-like orbitals, which often are diffuse (depending on what basis sets you used). This might be a reason why the HOMO-LUMO transition is not the lowest triplet transition...
-Pradeep

christof.haettig

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Re: 1st and 2nd triplet excitation using ESCF for a Platinum complex
« Reply #2 on: March 31, 2008, 11:51:31 AM »
The orbital energy differences are very crude approximations for excitation energies: it neglects any changes in the mean field upon the excitation. If orbitals are close in energy, it is quite common that the order of excited states changes between this simple estimate and a true TDHF or TDDFT calculation.

Christof