[Pw_forum] pbe with norm conserving pp convergence problem

[Peng Chen]

Dear Jia,

I checked those pp and there are not recommended cutoffs. When I use
occupation=fixed, the results are similar as those from occupation=smearing
(reach minimum at 80 Ry) . And the scf doesn't converge when ecutwfc=60 Ry.

Ecutwfc   energy     total force
50 -1129.7209 0.7937
60 no  convergence
70 -1136.6081 0.7066
80 -1137.3776 0.7059
90 -1137.3342 0.6997
100 -1136.9523 0.7056

On Mon, Sep 10, 2012 at 5:17 PM, Jia Chen <jiachenchem at gmail.com> wrote:

> Dear Peng,
>
> For AFM case, you can set tot_magentization = 0, for FM case, you need
> to know tot_magnetization from experiments or previous calculations.
> Or you can use the int(absolute magnetization) from you AFM
> calculations.
>
> Trying to converge total energy with respect to wave function cutoff
> is usually not a good idea. If you just want to choose a good cutoff
> energy for calculations, first thing you can do is to look into those
> pseudopotentials you are using. If you can find recommended cutoffs,
> you probably can just use the highest cutoffs in your system.
>
> Bests
> Jia
>
> On Mon, Sep 10, 2012 at 5:02 PM, Peng Chen <pchen at ion.chem.utk.edu> wrote:
> > Dear Dr.  Giannozzi,
> >
> > Thanks for your reply. I use smearing for computing the band structure in
> > afm and fm states. It looks there is still a lot to learn. If I use
> > occupation=fixed to calculate afm/fm states, shall I just set
> > tot_magnetization=0 or 1?
> >
> > If I didn't set ecutrho, the default value of ecutrho is 4*ecutwfc. So
> the
> > results are the same as the following, and the energy doesn't decrease
> > monotonically. I tried to decrease degauss to 0.005 Ry, I got the similar
> > results. What I can do to make the energy converge?
> >
> > ecutrho=4*ecutwfc
> > ecutwfc     energy            total force
> > 30 -1086.672528 1.335253
> > 40 -1119.972723 0.690327
> > 50 -1129.973333 0.690484
> > 60 -1134.622157 0.640747
> > 70 -1136.892534 0.617201
> > 80 -1137.666471 0.616635
> > 90 -1137.620919 0.610216
> > 100 -1137.238099 0.615361
> > 110 -1136.89911         0.62063
> > 120 -1136.866006 0.622763
> >
> > On Mon, Sep 10, 2012 at 3:45 PM, Paolo Giannozzi <giannozz at democritos.it
> >
> > wrote:
> >>
> >>
> >> On Sep 10, 2012, at 16:35 , Peng Chen wrote:
> >>
> >> > I tried to calculate an insulator Ni3V2O3 using pbe norm conserving
> >> > pp from pslibrary. But the energy related with ecutwfc is not
> >> > converged. It reaches minimum at ecutwfc=80 Ry. But when I fix
> >> > ecutrho=320 Ry and increase  ecutwfc, it starts to decrease
> >> > monotonically. I am not sure if the system reaches the convergence
> >> > at ecutwfc=80 Ry.
> >> > (smearing=mv, Degauss=0.01 Ry and kpoints = 4 4 3)
> >>
> >> if it is an insulator, why are you using smearing? Apart from this:
> >> with norm-conserving PP, ecutwfc is the only parameter defining
> >> the basis set. You should not set ecutrho.
> >>
> >> P.
> >> ---
> >> Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
> >> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> >> Phone +39-0432-558216, fax +39-0432-558222
> >>
> >>
> >>
> >>
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> >
> >
> >
> >
> > --
> >   Best Regards.
> >         Peng
> >
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> >
>
>
>
> --
> Jia Chen
> webpage: www.princeton.edu/~jiachen
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>



-- 
  Best Regards.
        Peng
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