[Pw_forum] TB09 metaGGA

Fri Oct 31 10:20:17 CET 2014

Dear Juanjo, 

From what I can remember:
- the meta-GGA kinetic terms are not saved in order to restart a nscf, at least up to the 5.0 version,
- the tools for building meta-GGA PPs are not available in QE.
However, I'm not sure using meta-GGA pseudos will solve your problem. Meta-GGA are known to have numerical instabilities such as the ones you met, in particular when then electronic density drop to a very low level as probably in your ionic crystal LiF, on the contrary with Si and C that form covalent structures.

You can have a look to this paper you probably know:
E.R. Johnson, JCP 131, 034111 2009

I don't believe a cure to you problem exists at the moment, 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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> 
> 
> >-----------------
> Pascal Boulet
> Aix-Marseille University 
> MADIREL Laboratory
> Avenue Normandie-Niemen 
> 13397 Marseille Cedex 20 
> Email: pascal.boulet at univ-amu.fr 
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