[CP2K:1965] Re: Geometry Optimisation / Frequency (general question)

[Jörg Saßmannshausen]

Hi Theo,

copy&pasta mistake:

first (for geo-opt and first frequency):
 EPS_SCF 1.0E-8

and then (only for the second frequency):
 EPS_SCF 1.0E-9

And yes, you were right in some respect, I originally started that all off 
with  EPS_SCF 1.0E-6 but right now I am using EPS_SCF 1.0E-8 right from the 
beginning as with higher values I had problems to find the minimum (i.e. more 
neg. frequencies).

The snip from the output file for the geo-opt:
eps_scf:                                        1.00E-08
eps_scf_history:                                0.00E+00
eps_diis:                                       1.00E-01
eps_eigval:                                     1.00E-05
 --------------------------------------------------------
p_mix:                                              0.40
G-space mixing a:                                   1.00
G-space mixing b:                                   0.00
work_syevx:                                         1.00
level_shift [a.u.]:                                 0.00

and of the freq.inp:

&VIBRATIONAL_ANALYSIS
   NPROC_REP 4
   DX 0.001
   &PRINT
     &PROGRAM_RUN_INFO ON
     &END
     &MOLDEN_VIB
     &END
   &END
&END

I remembered from your last reply that DX 0.001 is ok, so I did not mess 
around with that one.

One other question, number of replicas is the number of the CPUs used? Or did 
I get that wrong?

Thanks for the quick reply Theo!

On a more personal side, I hope that nobody you know was effected by the earth 
quake today in Italy!

All the best!

Jörg

On Montag 06 April 2009 Teodoro Laino wrote:
> 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
>
> 
-- 
*************************************************************
Jörg Saßmannshausen
Research Fellow
University of Strathclyde
Department of Pure and Applied Chemistry
295 Cathedral St.
Glasgow
G1 1XL

email: jorg.sassm... at strath.ac.uk
web: http://sassy.formativ.net

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