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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