[Pw_forum] TB09 metaGGA

Fri Oct 31 15:17:46 CET 2014

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" <melendez at unex.es> 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: melendez at unex.es
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" <melendez at unex.es> 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: melendez at unex.es
Web: http://materiales.unex.es/miembros/personal/jj-melendez/Index.html         ****************************    “All    those who look stupid actually are, as also are half of those who do not    look like” (F. de Quevedo)         ****************************

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Aix-Marseille University 
MADIREL Laboratory
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13397 Marseille Cedex 20 
Email: pascal.boulet at univ-amu.fr 
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: pascal.boulet at univ-amu.fr
Tel. +33 413 55 18 10
Fax  +33 413 55 18 50
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