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Thomas
thomaspijper@hotmail.com

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,
>>>