Ceilidh ... Re^4: How to get rid of Imaginary Frequencies.....

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Re^4: How to get rid of Imaginary Frequencies.....

Dear Thom,
I am eager to know about your statement "When I start a geometry optimization form your structure, I find that the geometry you use in your Hessian calculation isn't a minimum geometry yet.".. Thomas how do you get an idea that it is a transition state BEFORE EVEN running hessian calculation? is there any method I can use to do know its local minimum nature before running a COSTLY hessian calc.?
Yes, the file has imaginary freqs. but I would add here that I DID run RUNTYP=OPTIMIZE, before going for HESSIAN calc. And when I completed the OPTIMIZATION job, I got the message, equilibrium geometry reached. What I knew is that I MUST run hessian calc. to know if it is a global minimum or not..
However, I read somewhere that we can somehow find the global/local minimum nature by looking at the structure.. PLEASE HELP..

Regards,

On Thu Feb 7 '13 11:58am, Thomas wrote
--------------------------------------
>Dear Siddheshwar,

>When I start a geometry optimization form your structure, I find that the geometry you use in your Hessian calculation isn't a minimum geometry yet. You must always first optimize your structure with a RUNTYP=OPTIMIZE job before you can obtain a Hessian free of imaginary frequencies.

>Note that you should always use the exact same settings during the optimization and Hessian calculation -- basis set, functional, and accuracy settings should be identical between the two. This is because different settings typically lead to different minima. A minimum calculated with pc-2 is different from a minimum calculated with 6-31G(d,p), and the Hessian will only be free of imaginary frequencies when the geometry really is in a minimum.

>Hope this helps.
>
>
>Kind regards,
>Thom
>
>
>
>
>
>On Thu Feb 7 '13 6:54am, Siddheshwar Chopra wrote
>-------------------------------------------------
>>Dear Thom,
>>As asked by you, please find attached a sample file, which contains four imaginary frequencies..

>>Regards,
>>
>>
>>
>>
>>On Wed Feb 6 '13 11:36am, Thomas wrote
>>--------------------------------------
>>>Dear Siddheshwar,

>>>Could you please post the complete output of your Hessian calculation? This would allows us to see what kind of imaginary frequencies you're finding.
>>>
>>>
>>>Kind regards,
>>>Thom
>>>
>>>
>>>
>>>On Wed Feb 6 '13 10:56am, Siddheshwar Chopra wrote
>>>--------------------------------------------------
>>>>Dear Sir,
>>>>This in regard to my problems with getting rid of imaginary frequencies in the vibrational data. I have tried changing the basis sets, changed the ITOL, ICUT values... Please suggest me what should I do to ge trid of imaginary frequencies?? Currently I am trying out PC-2 basis set. A sample input commands are as follows:

>>>> INPUT CARD> $SYSTEM MEMORY=12065831 aoints=dist TIMLIM=525600 KDIAG=1 $END
>>>> INPUT CARD> $CONTRL INTTYP=HONDO ICUT=11 ITOL=30 RUNTYP=HESSIAN SCFTYP=RHF $END
>>>> INPUT CARD> $CONTRL DFTTYP=B3LYP COORD=UNIQUE NZVAR=132 $END
>>>> INPUT CARD> $CONTRL MAXIT=10000 MOLPLT=.t. PLTORB=.t. $END
>>>> INPUT CARD>! $CONTRL EXETYP=CHECK $END
>>>> INPUT CARD> $BASIS GBASIS=N31 NGAUSS=6 NDFUNC=1 NPFUNC=1 $END
>>>> INPUT CARD> $STATPT opttol=10E-7 NSTEP=200 Method=GDIIS HSSEND=.TRUE. $END
>>>> INPUT CARD> $SMP HTTFIX=.f. $END
>>>> INPUT CARD> $p2p p2p=.t. mxbuf=2048 dlb=.t. $END
>>>> INPUT CARD> $SCF dirscf=.t. fdiff= .f. diis=.t. $END
>>>> INPUT CARD> $DFT HFX(1)=0.15 $END
>>>> INPUT CARD> $ZMAT DLC=.t. AUTO=.t. $END
>>>> INPUT CARD> $FORCE NVIB=2 $END

>>>>Please help me.
>>>>
>>>>
>>>>Regards,
>>>>

Thu Feb 7 '13 12:54pm

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