[Pw_forum] To set Kinetic energy cut off and ecutrho

[Giovani Faccin]

Dear Yuva,

I believe you should test the convergence of the total energy as those
parameters vary. Usually, ecutrho should be between 8 to 14 times the value
of ecutwfc, depending on the material. For example, you could run a scf
calculation using, say, ecutwfc=30, ecutrho=300, then again with ecutwfc=40,
ecutrho=400 and so on, and check the total energy convergence. Then given a
value of ecutwfc, you can vary ecutrho to see which values lead to
convergence. This is needed in order to find a setup that mixes precision
with computational cost well. If, on the other hand, you don't care about
computational cost, then you could use, say, ecutwfc=200 and ecutrho=2800
and I'm pretty sure you'll have a well converged calculation, altough it'd
take a very long time to evaluate it (or not, if you can use a very powerful
computer).

Best,

Giovani M. Faccin
UFMS/Unicamp - Brazil



2011/6/8 yuva rani <syuva2987 at gmail.com>

> On 6/8/11, yuva rani <syuva2987 at gmail.com> wrote:
> > I am trying to relax a gold surface consisting of 112 atoms. I
> encountered
> > a
> > error in the output file as negative rho (up, down). I need the guidence
> of
> > the ecutwfc for gold and how to set this value.
> > *Thank you and Regards,
> > **
> > ** S.Yuva
> > ** Physics Department
> > ** Bharathiar University.*
> >
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-- 
Giovani
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