Dear Juanjo,
As far as I know, metaGGAs are like GGAs for gaps: there are not accurate. For
getting good gaps you have to switch to hybrid functionals or GW formalism
(not implemented in QE though). Depending on what you want to do, of course,
and if you know the gap value you may try this: optimize with a standard GGA
functional, run a nscf calculation and if the gap is not totally closed up then
operate a rigid band shifting for further properties calculations. This is a
bit brute force...
If you do not know the gap value: run a hybrid single point calculation on the
GGA optimized structure.
As Yves said, there are not so many options...
Pascal
"Juanjo Meléndez" <[email protected]> wrote:Dear Yves Thanks a lot for your
comments. Unfortunately, I need a good description ofgaps to calculate optical
absorption, and hybrid functionals are prohibitive forthe supercells that I
need to use. That is why I started to try withmetaGGA. I will have a look to
the paper you mention (which I did not know, by theway, thanks!) for more
ideas... Take care Juanjo From: Yves Ferro Sent: Friday, October 31, 2014 10:20
AMTo: PWSCF Forum Subject: Re: [Pw_forum] TB09 metaGGA DearJuanjo, From what I
can remember:- the meta-GGA kinetic terms are notsaved in order to restart a
nscf, at least up to the 5.0 version,- the tools for building meta-GGA PPs are
not availablein QE.However, I'm not sure using meta-GGA pseudos will solveyour
problem. Meta-GGA are known to have numerical instabilities such as theones you
met, in particular when then electronic density drop to a very lowlevel as
probably in your ionic crystal LiF, on the contrary with Si and C thatform
covalent structures.
You can have a look to this paper you probablyknow:E.R. Johnson, JCP 131,
0341112009
I don't believe a cure to you problem exists at themoment, except by changing
the functional to a GGA one.
Best regards,
Yves.
Le 31 oct. 2014 à 09:26, Juanjo Meléndez a écrit :
Hi Pascal Thanks for replying. I agree with you that building a PP
consistent with the metaGGA functional would solve most of the instability
problems. But I do not have *any* experience building PPs (which, by the way,
seems to be not trivial to me, even less trivial for metaGGA), so I followed
http://dx.doi.org/10.1016/j.cpc.2013.02.020 and tried the trick. I was just
wondering if any general strategy for convergence exists. Regarding point
2, I asked one of the authors of the aforementioned paper and he declared not
the have seen such a problem before, so I guess that the kinetic terms are not
responsible. I have overcome the problem by using a dense kpoints path already
in scf calculations and calculating the bands without the standard
intermediate nscf run, but it would be nice if the developers could have a
look and check. Again, thank you very much for your interest. Juanjo
Juan J. Meléndez
Associate Professor
Department of Physics · University of Extremadura
Avda. de Elvas, s/n 06006 Badajoz (Spain)
Phone: +34 924 28 96 55
Fax: +34 924 28 96 51
Email: [email protected]
Web: http://materiales.unex.es/miembros/personal/jj-melendez/Index.html
From: Pascal BOULET Sent: Thursday, October 30, 2014 7:15 PM To: PWSCF
Forum Subject: Re: [Pw_forum] TB09 metaGGA hello, I have never
tried meta-GGA functionals with QE, so I am guessing. For point 1, one
possible reason is the inadequacy between the pseudo potential and the
functional. I guess you have build a special pseudopotential for this
functional. Point 2: Could it be because the meta-GGA kinetic terms are not
saved in the checkpoint file and hence not readable when doing the nscf?
Pascal "Juanjo Meléndez" <[email protected]> wrote: Hi all
I am starting to work with metaGGA functionals in QE (v. 5.1 +
libXc), following Èric Germaneau and colleagues’ work
(http://dx.doi.org/10.1016/j.cpc.2013.02.020). I know that metaGGA is little
tested, but I would be pleased if somebody could answer a couple of
questions: 1) Convergence is quite tricky. Up to know, I got some
results in simple systems using a very small mixing_beta (within 0.01–0.05),
not too many bands (just one or two conduction bands, never converged for
more bands) and restarting from a previously fully converged calculation. I
got results only for carbon, silicon and germanium, never got any
convergence for any binary simple compound (like LiF). Does anyone have
additional hints for metaGGA calculations to converge? 2) In addition,
I get something wrong with nscf calculations. After convergence of a scf
run, I get a list of bands at each k-point, as usual –nothing strange here.
Then I made a path of k-points to get the band structure and run a nscf
calculation. This finishes fine as well, but the bands are not only
different from those from the scf calculations, but also unrealistically
high. I am attaching the input and output files for both the scf and nscf
runs, as well as a couple of eigenval.xml files taken after nscf. Does
anybody know how to manage this? Or could this be a bug in the code?
Thanks a lot in advance Take care Juanjo Juan J.
Meléndez
Associate Professor
Department of Physics · University of Extremadura
Avda. de Elvas, s/n 06006 Badajoz (Spain)
Phone: +34 924 28 96 55
Fax: +34 924 28 96 51
Email: [email protected]
Web: http://materiales.unex.es/miembros/personal/jj-melendez/Index.html
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Aix-Marseille University
MADIREL Laboratory
Avenue Normandie-Niemen
13397 Marseille Cedex 20
Email: [email protected]
Tel. +33 413 55 18 10
Fax +33 413 55 18 50
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Pascal Boulet
Aix-Marseille University
MADIREL Laboratory
Avenue Normandie-Niemen
13397 Marseille Cedex 20
Email: [email protected]
Tel. +33 413 55 18 10
Fax +33 413 55 18 50_______________________________________________
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