[CP2K:1964] Geometry Optimisation / Frequency (general question)

Teodoro Laino teodor... at gmail.com
Mon Apr 6 17:22:54 UTC 2009

Hi Jörg,

I'm a bit confused:
> I have managed to get a converged geometry with these parameters:
>     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
> 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!


> 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!
> Jörg

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