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Slawomir Janicki
slawomir.janicki@comcast.net

Visualization is difficult when I have hundreds of files to work up. I will try the other ideas first.

Slawomir

On Sun Nov 22 '09 8:34pm, Alex Granovsky wrote
----------------------------------------------
>Hi Slawomir,

>Sometimes, one can get small negative (imaginary) frequencies
>that actually correspond to rotations or translations. This is
>not too unusual with numerical Hessians. This can be typically
>avoided using nvib=2 with smaller vibsiz (e.g., 0.005 or so)
>while increasing overall precision of calculations (more precise
>integrals, DFT grids, tighter cutoffs throughout, etc...). However,
>this usually does not seriously affect the computed values of "real"
>vibrational frequencies. It is also very helpful to visualize
>the vibration of question, and also examine T+R vibrations before
>projection (i.e., with PROJCT=.f.).

>However, what looks really strange are your numbers for other frequencies;

>Analytic:
>>            237.43
>>            237.43
>>            268.28
>>            544.38

>Numeric:
>>            202.41
>>            202.51
>>            352.25
>>            352.31

>Is this exactly the same system? at the same geometry?
>and exactly the same type of computations?

>Regards,
>Alex
>

>On Sun Nov 22 '09 5:38pm, Slawomir Janicki wrote
>------------------------------------------------
>>Hi,

>>I was comparing analytical and numeric methods for hessian runs, and I found that in one case the numeric methods produced negative frequencies:

>>geometry optimization run:
>> $STATPT NSTEP=500 HSSEND=.F. TRMIN=0.01 METHOD=GDIIS NOREG=5
>> OPTTOL=0.0000001 $END

>>hessian runs:
>>analytical:
>> $FORCE METHOD=ANALYTIC PROJCT=.TRUE. VIBANL=.TRUE. PRTSCN=.TRUE. SCLFAC=1 $END
>>gave:
>>                          1           2           3           4           5
>>       FREQUENCY:         0.00        0.00        0.00        0.00        0.00  

>>and

>>          FREQUENCY   ENTROPY   %-CONTRIBUTION
>>          ---------   -------   --------------
>>            237.43     1.822           26.50
>>            237.43     1.822           26.50
>>            268.28     1.607           23.38
>>            544.38     0.556            8.09
>>
>>
>>numeric 1 step:
>> $FORCE PROJCT=.TRUE. VIBANL=.TRUE. PRTSCN=.TRUE. SCLFAC=1 METHOD=NUMERIC
>> NVIB=1 $END
>>gave:
>>                          1           2           3           4           5
>>       FREQUENCY:        14.32 I      0.00        0.00        0.00        0.00  

>>and

>>          FREQUENCY   ENTROPY   %-CONTRIBUTION
>>          ---------   -------   --------------
>>            207.78     2.063           29.17
>>            212.70     2.020           28.56
>>            355.72     1.141           16.13
>>            355.99     1.140           16.11

>>numeric 2 step:
>> $FORCE PROJCT=.TRUE. VIBANL=.TRUE. PRTSCN=.TRUE. SCLFAC=1 NVIB=2
>> METHOD=NUMERIC $END
>>gave:
>>                          1           2           3           4           5
>>       FREQUENCY:        14.14 I      0.00        0.00        0.00        0.00  

>>and

>>          FREQUENCY   ENTROPY   %-CONTRIBUTION
>>          ---------   -------   --------------
>>            202.41     2.111           29.15
>>            202.51     2.110           29.13
>>            352.25     1.156           15.96
>>            352.31     1.156           15.96

>>Is there a way to avoid this? I need to rely on numeric requencies when I can't use analytical hessian.

>>Slawomir