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Different frequency obtained by hessian calculation of the same molecule on different programs


Hi to everyone,
I need to understand if a systhematic error exists calculating UV/vis spectra in organic dyes.
At the beginning i tried to obtain an optimized structure that could be a minimum of the PES, and i noted that computing an hessian on a optimized structure (semi-empiric model-AM1) of Rodamine 123, i got all positive frequencies using both Gaussian and Spartan but two negative using firefly.
So, i would like know if there is a reason (theory level and coordinates were the same for both, of course) for that and how can i decide whether this stucture is a minimum or not.
You'll find attached the input files.
thanks for your valuable help

Enrico Chiavazza

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