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#1 2026-05-28 00:12:59
- wham09
- Member
- Registered: 2025-09-19
- Posts: 64
Problem of non-equilibrium solvation in SF-TDA
Dear Prof. Lu,
I have tested an organic molecule (neutral, singlet) in ORCA's spin-flip (SF-TDA) calculation.
Below is the general input command block that I used:
! BHANDHLYP def2-TZVP tightSCF CPCM(DMSO)
%cpcm xfeps 0.5 end
%TDDFT
SF TRUE
NROOTS 10
END
* xyz 0 3
...
As a result, the spin-flip ground-state was the singlet (as expected), and the spin-flip first excited-state shows S^2 of roughly 1.1, which seems to indicate the singlet diradical species.
My question is the following: When I do SF-TDA, the initial reference state is triplet, not singlet. Then, does the "slow" portion of solvation (that is fixed for non-equilibrium solvation calculation of spin-flip states) correspond to the triplet? If this is true, wouldn't this be unphysical, because in reality the slow portion of solvation should be that of the singlet ground-state?
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#2 2026-05-28 00:38:54
Re: Problem of non-equilibrium solvation in SF-TDA
I don't exactly know how ORCA deals with solvation effect for SF-TDA situation, but I think your opinion is likely correct, it indeed may be unphysical.
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#3 2026-05-28 01:37:49
- wham09
- Member
- Registered: 2025-09-19
- Posts: 64
Re: Problem of non-equilibrium solvation in SF-TDA
Dear Prof. Lu,
Again, thank you for the swift reply.
Your answer concerns me though, because if I'm correct, the general reliability of SF-TDA for solution-phase reactions becomes questionable.
Could you maybe recommend a route to communicate about this topic and find solutions? I do know that a lot of ORCA discussions are ongoing in Keinsci forum, but I'm not confident that an English thread (or a poorly translated Chinese thread) will be taken seriously there...
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