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Re: excited state geometry opt and intersystem crossing

sanya
sanya@photonics.ru

> $contrl scftyp=rhf DFTTYP=BLYP CITYP=cis runtyp=OPTIMIZE COORD=UNIQUE $end
> $cis nstate=1 istate=1 MULT=1 $end

It's easy: just remove DFTTYP=BLYP

>My question besides this error is: if intersystem crossing is encountered in firefly with CIS, what other methods I can use for 76 atom organic system to optimize excited state and (maybe) verify minimum with frequency calculations? Or systems with intersystems crossing can not fundamentally be described computationally at all?

What do you mean by intersystem crossing? The usual meaning is transitions between states of different multiplicity due to spin-orbit coupling. However, I am afraid you mean (avoided) crossing of PESs of the same multiplicity (say, two singlet PESs). This case cannot be treated properly by single-reference methods, such as CIS and TDDFT. MCSCF is recommended in this case, and Firefly is an excellent tool for this purpose. Within FF, you can optimize the geometry of a desired excited state (either in state-averaged or state-specific mode) or find conical intersections.

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