Recently I optimized the geometry of a molecule with C2v symmetry using SA2-MCSCF(10,10)/6-31G*, however, the optimized geometry is no longer symmetric (it can be seen clearly from the bond distances of the benzene moiety) and has a negative frequency (about -74i). Then I further optimize the geometry following the negative frequency and a stationary point is obtained without negative frequency. However, the symmetry is further destroyed. I'm confused with this result and I think the optimzied geometry is unreasonable. Is it because the active space is not large enough? I have also try to increase the active space to (12,12), although the frequency calculation has not completed, the optimized geometry by SA2-MCSCF(12,12)/6-31G* is similar to that of SA2-MCSCF(10,10)/6-31G*.
I attach the output files from SA2-MCSCF(10,10)/6-31G*.
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[ SA2-MCSCF10e10o-opt.zip ]