Slawomir Janicki
slawomir.janicki@comcast.net
Slawomir
On Mon Nov 23 '09 4:29am, Slawomir Janicki wrote
------------------------------------------------
>The system is the same, the Hessian calculations were done at the final geometry from the geometry optimization run.
>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