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Vladimir A. Mironov
vladimir.a.mironov@gmail.com

Also, do you really need so small value of OPTTOL? I guess, you could safely increase it by 1-2 orders of magnitude.

And, finally, I don't recommend you to calculate hessian before optimization. It will take great amount of time without any significant improvement. Remove HESS=CALC from STATPT group.

There are some unclear issue. On which stage your calculation failed? First iteration converges well with the changes above implemented.
How have you obtained the initial structure? It is highly recommended to use structure which is as close as possible to optimal one.

On Wed Dec 15 '10 3:53pm, Danas wrote
-------------------------------------
>Dear all,
>I tried to optimize  and to calculate the vibrational nodes for a carbocation of a relatively small molecule, in one step, but I got the error:
>SCF IS UNCONVERGED, TOO MANY ITERATIONS
>---------------------------------------
> *** NO FORCE FIELD, SCF DOES NOT CONVERGE AT VIB0 POINT
>---------------------------------------
> EXECUTION OF FIREFLY TERMINATED ABNORMALLY

>I used the following input:
>! ================================================================
>! Input file for Firefly
>! ================================================================
> $CONTRL SCFTYP=RHF RUNTYP=OPTIMIZE MAXIT=500 MULT=1 COORD=UNIQUE ICHARG=1 $END
> $CONTRL DFTTYP=B3LYP1 $END
> ! $CONTRL EXETYP=CHECK $END
> $SYSTEM TIMLIM=6000 MEMORY=8000000 $END
> $BASIS GBASIS=N31 NGAUSS=6 $END
> $BASIS NPFUNC=1 NDFUNC=1 $END
> $BASIS DIFFSP=.TRUE.  $END
> $STATPT OPTTOL=1e-006 NSTEP=500 HESS=CALC IHREP=10 HSSEND=.TRUE. $END
> $FORCE VIBANL=.TRUE. $END
> $DATA
>Molecule specification
>C1

>While for small molecules (acetone, benzene, ethanol - of course, in the input file  without ICHARGE), firefly worked properly , for the molecule with that you may see in the attachment I got the error above. Also, it was a very time consuming process.
>My goal is to find the vibration nodes (for the infrared spectra) of the molecule(s) using DFT with the basis set 6-31+G(p,d).
>I still struggle to find a way in order to speed-up the process of calculation and how to avoid the error. I think that there is something superfluous in my input file.
>Thank you in advance.
>

[ This message was edited on Thu Dec 16 '10 at 12:04pm by the author ]