[Pw_forum] TB09 metaGGA

Fri Oct 31 17:38:45 CET 2014

> you have to  switch to hybrid functionals or GW
> formalism (not implemented in QE though).

*both* implemented in QE, for the sake of accuracy...:-)
Have a nice we
G.

On Friday, October 31, 2014 03:17:46 PM Pascal BOULET wrote:
> 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 MelÃ©ndez" <melendez at unex.es> wrote:Dear YvesÂ 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.Â I will
> have a look to the paper you mention (which I did not know, by theway, thanks!) for more ideas...Â Take careÂ JuanjoÂ From: Yves Ferro Sent: Friday,
> October 31, 2014 10:20 AMTo: PWSCF Forum Subject: Re: [Pw_forum] TB09 metaGGAÂ DearJuanjo,Â Â 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 Ã  09:26, Juanjo MelÃ©ndez a Ã©crit :
>         Hi Pascal  Â   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.   Â   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.   Â   Again, thank you very much for your interest.  Â   Juanjo  Â   Juan J.  MelÃ©ndez Associate Professor
> Department of Physics Â· 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      Â     From: Pascal BOULET   Sent: Thursday, October 30, 2014 7:15 PM 
> To: PWSCF Forum   Subject: Re: [Pw_forum] TB09 metaGGA  Â       hello,  Â   I have never tried meta-GGA functionals with QE, so I am guessing.   Â  
> 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.  Â   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  Â     Â   "Juanjo MelÃ©ndez" <melendez at unex.es> wrote:              Hi all    Â     I am starting to work with metaGGA functionals in QE (v.   
> 5.1 + libXc), following Ãˆric Germaneau and colleaguesâ€™ 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:    Â     1) Convergence is quite tricky. Up to know, I got some    results
> in simple systems using a very small mixing_beta (within 0.01â€“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?    Â     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
> â€“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?    Â     Thanks a lot in advance    Â     Take care    Â     Juanjo    Â     Juan J.    MelÃ©ndez Associate 
Professor
> Department of Physics Â· 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    Â     ****************************    â€œAll    those who look stupid
> actually are, as also are half of those who do not    look likeâ€ (F. de Quevedo)    Â     ****************************
> 
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> >-----------------
> 
> Pascal  Boulet
> Aix-Marseille University
> MADIREL Laboratory
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> Email: pascal.boulet at univ-amu.fr
> Tel.  +33 413 55 18 10
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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
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