[CP2K:1964] Geometry Optimisation / Frequency (general question)
Teodoro Laino
teodor... at gmail.com
Mon Apr 6 17:22:54 UTC 2009
Hi JÃ¶rg,
I'm a bit confused:
> I have managed to get a converged geometry with these parameters:
> &GEO_OPT
> MINIMIZER BFGS
> MAX_ITER 300
> MAX_DR 3.00E-4
> RMS_DR 1.50E-4
> MAX_FORCE 4.50E-5
> RMS_FORCE 3.00E-5
> &BFGS
> &END
> &END GEO_OPT
>
> and
> EPS_SCF 1.0E-8
>
so you used 1.0E-8 for GEO_OPT. and then you did with the same EPS_SCF
the frequency analysis and you got
a neg. freq. then you decreased the value to 1.0E-8 (which is the same
as before :-) ) and it solved your issue..
well.. then you were just lucky and you may have had a problem with the
interaction of neutrinos with your CPU ;-).
I suspect your first EPS_SCF was the default 1.0E-6. right?
in any case (general rule) if the numerical frequencies are computed by
finite differences of course you need to
be careful, especially for low-frequencies. Infact, depending on DX and
EPS_SCF you may just observe numerical
noise for small frequencies.
You did it right then!
Cheers
Teo
> Using the same EPS_SCF 1.0E-8 for the frequency analysis, I get one neg. freq.
> at -42.76 1/cm. However, as I remembered from the ADF program, it might be
> actually beneficial to use a tighter criterion for the numerical frequency
> analysis, so I decreased the value to EPS_SCF 1.0E-8 and loo! now that neg.
> frequency has gone.
>
> Is that generally a good idea to run the frequency calculation a bit tighter
> than the geometry optimisation or was I just lucky?
>
> I just try to get the grips of the program, hence the question.
>
> Thanks for your help!
>
> JÃ¶rg
>
>
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