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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