As of recently, we have begun working with spin-flip methods in our group to describe some diradicals (some have triplet and others singlet ground states, we would like to be sure our previous method identifies the right one) and the privilege has fallen upon me to discover how to invoke these methods in Q-Chem. I think I figured out the SF-XCIS and SF-TDDFT methods, but I am still having some problems with others and I hope you can help me with them.
The first one concerns the SF-CI methods (i.e. CIS, CISD, CISDT). I would like to invoke SF-CIS just as a test, but I only get triplet and quintet states with an input that contains:
Are there other keywords I should add? Additionally, how do I transform this into CISD or CISDT? I found in the manual it seems to be possible, but I couldn’t immediately find how and some tests didn’t go very well.
As a second question: how should I specify the number of states of the irreproducible representations for molecules with the D∞h point group, e.g. in EOM-SF-CC calculations? Maybe this is a trivial question, but I couldn’t quite figure it out for the ∞ point groups.
Thanks in advance for any info you can supply.
Kind regards, Jochen