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Alex Granovsky
gran@classic.chem.msu.su

how large are these imaginary frequencies? If they are small,
this could be an artifact from numerical hessian calculations.
You can use $force nvib=2 $end to improve precision of the computed
hessian and frequencies. I'd also strongly suggest you to visualize
these "bad" frequencies to understand their origin. Another thing
to try is use larger and better basis set.  

Kind regards,
Alex Granovsky



On Tue Apr 24 '12 12:58pm, Adebayo A. Adeniyi wrote
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>Dear all Firefly Users,

>I optimized my metal organic compounds of Ru metals (derivatives of anticancer called RAPTA) using external basis set with PBE0 functional. The basis set for the Ru, Cl, P is SBKTC with ECP while other atoms have 6-31g. But after obtainig the optimized geometry, I extracted the optimized geometry using Open Babel and proceed to frequency calculation using RUNTYP=HESSIAN, GUESS=READ and HESS=CALC, but against my expectation, almost all the supposed stable moleculed were having their first frequency as Imaginary. I want to know what is wrong since the initial geometry of some is from crstal structure.