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numbering of states with ALDET-MCSCF, (X)MCQDPT2, and Conical Intersections

Bernhard Dick

I am getting confused with how Firefly renumbers states. I am searching for a conical intersection between the states S0 and T1 of a system with an even number of electrons. I encounter problems with convergence of MCSCF unless I include also the next two states in the MCSCF. Therefore, i am using ALDET with

NSTATE=4 WSTATE(1)=1,1,1,1  PURES=.F.

to get state-averaged MCSCF. The states are calculated in the order S0, T1, S1, T2

I start the search for conical intersection with these optimized orbitals, and set ISTATE=1 in $MCSCF and JSTATE=2 in $MCAVER. This should give me the crossing between S0/T1. Then I stop the calculation after NSTEP=100 (convergence is not obtained, but the energies do not change much, and the gap is 2-3 mHartree). Since Firefly at this point does not tell me the engergies of all 4 states, I do an extra MCSCF with the last geometry and orbitals, and it turns out that the crossing obtained is between S1 and T2, i.e. between states 3 and 4!

I used NTRACK=4 in $MCSCF and the group
according to the manual.

Finally, I want to calculate MCQDPT2 corrections at the final geometry. But when I add the group


I do not get the corrections for the 4 states calculated with ALDET, but for the lowest 4 singlet states (although MULT was not set in $CONTRL). How can I do the MP2-correction for the same states that are calculated in the MCSCF?

with best regards,

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