[QE-users] Occupation calculation - epsilon.x code

[Michal Krompiec]

Dear Andrea,
It would be great if you could share the new epsilon.f90 code. If it takes
time to merge it with the develop branch, can you put it in a separate one
for now?
Best regards,
Michal Krompiec
Merck KGaA, Darmstadt, Germany

On Wed, 8 Jul 2020 at 20:31, Andrea Ferretti <andrea.ferretti at nano.cnr.it>
wrote:

>
> Dear Anibal,
>
> you are right, it seems calculation="occ" is documented but no longer
> there. As far as I understand, the reason is exactly that it is preferred
> to directly compute the quantity of interest and perform convergence
> checks on it (epsilon.x should be fast enough, though).
>
> Regarding the anysotropy: as far as I remember epsilon.x does not
> implement symmetries, meaning that kpts need to span the whole BZ.
> If you run a scf and a nscf calculation using pw.x and does not pay
> attention to this (meaning you have not set nosym=.T. noinv=.T.), kpts
> will be symmetrized and only the IBZ wedge will be sampled. In turn this
> can lead to spurious anysotropy (besides non-correct results).
>
> hope it helps
> Andrea
>
> BTW: I have a newer version of epsilon.f90 contributed by Tae-Yun Kim
> (Seoul National University, South Korea) which fixes a number of these
> issues. Just haven't found the time to include it in the official
> distribution.
>
> >
> > The epsilon.x manual (in the PP/DOC folder) shows the possibility of
> calculating occupations using the key "occ" within the epsilon.x. It is
> > emphasized to be a good tool to analyze convergency against the
> broadening parameter and the k points sampling. However, the "occ"
> > calculation is not implemented (at least in the version I'm using -
> 6.4). Such a calculation was implemented with other packages?
> >
> > If not, is there a way of verifying the convergence other than
> explicitly changing the broadening and k points sampling?
> >
> > I'm working with an AuAl alloy, trying to evaluate the dielectric
> function. Using epsilon.x I've got anisotropic behavior that I was not
> > expecting for. Working with pure systems (Au and Al) I concluded that
> reducing conv_thr increases the epsilon.x output precision, returning
> > the isotropic behavior of the dielectric function. Therefore, to the
> alloy (with 12 atoms in the cell), I increased both the conv_thr (1e-13)
> > and k points (14 14 14). I still got the anisotropy. Should I go further
> (calculations with my actual computing power are becoming very time
> > and memory consuming)?
> >
> > Thanks in advance!!
> >
> > Anibal Bezerra
> > The Federal University of Alfenas
> >
> >
>
> --
> Andrea Ferretti, PhD
> S3 Center, Istituto Nanoscienze, CNR
> via Campi 213/A, 41125, Modena, Italy
> Tel: +39 059 2055322;  Skype: andrea_ferretti
> URL: http://www.nano.cnr.it
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