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On 22 Apr 2022, at 18:55, Nikunj Kumar nkk749 a gmail.com <owne= r-chemistry*ccl.net> wrote:

=EF=BB=BF
Sent to CCL by: "Nik= unj Kumar" [nkk749..gmail.com]
Dear all,
I am working on an interesting catalyst system which has non-innocent lig= and. I
have optimized the triplet structure using the ORCA 4= .2.1 employing the TPPSh
functional. I was expecting the S^= 2 value to be around 2.0 but it came out to
be 2.71. Can we= consider this as a triplet? Is this value reliable, if not how
<= span>can we get rid of the spin contamination.

Thanks
Nikunj Kumar

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Dear Nikunj, in addition to the previous comments: If you have a broken symmetry state, you can get and analyze the "corresponding orbitals" with ORCA by adding the following keyword to your input: ! UCO For a description on how to look at the UCOs see reference: Neese, F., Definition of corresponding orbitals and the diradical character in broken symmetry DFT calculations on spin coupled systems. Journal of Physics and Chemistry of Solids 2004, 65 (4), 781-785. Best wishes, Christoph PS: Also, I encourage you to upgrade to ORCA 5, which shows significantly improved robustness and speedup, in particular for hybrid functionals.

Sent to CCL by: Kathrin Helen Hopmann [kathrin.hopmann]_[uit.no] Dear Nikunj Kumar, Have you checked where the unpaired spin is located? 2.71 sounds as if you may have a "broken symmetry triplet", which would imply excess beta spin in one place of the molecule (the ligand?) and excess alpha spin in another (for example a metal). If you have 1 unpaired beta spin on the ligand and 3 unpaired alpha spins on the metal you would get a broken symmetry triplet with a higher than expected S^2 value (the actual computed spin populations are probably smaller, for example 0.6 on ligand and 2.6 on metal). In my experience, functionals with less (or no) HF exchange are more likely to give pure spin states (= less spin contamination). So if you are certain that the electronic structure should be a pure triplet, you could go for another (pure) functional and see what solution you get. If you obtain the pure triplet (2 unpaired alpha spins), you could try to also find the broken symmetry triplet with the other functional (this can be done by using the broken symmetry TPSSh electronic structure or the quintet electronic structure as input for the optimization). In that way you could get an idea if the pure or the broken symmetry triplet is lower in energy. It may be noted though that the energy of a broken symmetry state is approximate (you would have to do a spin projection of the energy to get a more correct value). You should probably also check the energy of the singlet as well as the quintet, just to be sure that none of these is lower than the triplet. And of course, as alwa! ys, different functionals may give you different answers as to what is the preferred electronic state. best regards, Kathrin -----Original Message-----

Sent to CCL by: "Nikunj Kumar" [nkk749..gmail.com] Dear all, I am working on an interesting catalyst system which has non-innocent ligand. I have optimized the triplet structure using the ORCA 4.2.1 employing the TPPSh functional. I was expecting the S^2 value to be around 2.0 but it came out to be 2.71. Can we consider this as a triplet? Is this value reliable, if not how can we get rid of the spin contamination.