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

[Teodoro Laino]

Hi Jörg,

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!
>
> Jörg
>
>