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negative frequencies after CI opt and huge PUNCH file

Jonas Baltrusaitis
jonas-baltrusaitis@uiowa.edu


I have somewhat awkward problem: I did CI geometry optimization and frequency calculations. All of my comparable HF geometries had no negative frequencies, whereas all of the CI ones had one or two low negatives. Interestingly, all the SP upon the atom displacement are of higher energy than the initial one so I do not know how do these negatives come about...
Anyway, I decided to do NVIB=2 and see if it's some accuracy error. The problem is that I have generated a 5 Gb PUNCH file and nothing can open it to extract data for MOREAD. Of course, IRCDATA provided $VIB of NVIB=1 for restart.
So I have two questions:
-what about those negative frequencies after CI opt? Numeric error and NVIB=2 would solve it or reoptimization is necessary?
-how do I extract last orbitals for MOREAD form that gianormous file? Any Linux based commands/tricks? I will need it for either geometry reoptimization or NVIB=2 anyways

thanks

Jonas


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