[QE-users] On the use of the modified Becke-Johnson (TB09) functional

[Fabrizio Ferrari]

Dear Fabio,
I added some lines in the attached file 'Modules/xc_mgga_drivers.f90' so
that, by replacing it with the original one, you should be able to set the
c parameter in tb09. You can do it directly into that module by setting the
initial value of cc_param or in any part of the program by calling the
routine 'set_cc_for_tb09(xx)' (but in case you may need to adjust the
module dependencies).
Before the compilation you need to add the '-lxcf03' in LD_LIBS in the
make.inc file
Hope it helps,
Fabrizio

On Wed, Nov 6, 2019 at 8:36 PM Fabio Costa <fabiocosta4 at hotmail.com> wrote:

> Dear users and developers
>
> After some more attempts to use the TB09 functional, I ended up finding
> this previous post:
> https://lists.quantum-espresso.org/pipermail/users/2019-April/042619.html ,
> and after changing v_of_rho.f90, the code is now able to end without any
> error.
>
> In my attempts, I'm performing the calculations as an initial scf run with
> a PBE pseudopotencial, and then another scf run, now with restart_mode =
> 'restart' and input_dft = 'MGGA_X_TB09'. By following this procedure, as
> described in E. Germaneau's paper, the calculations do converge.
>
> The issue now is that the gap energies I'm finding are very large. For
> example, for silicon, the calculations result in a 2.8 eV gap, larger even
> than the results presented in the paper, where the values ranged between
> 1.9 to 2.3. Despite the large gaps, the band structure and DOS agree well
> with the ones obtained with PBE.
>
> Is there any way to improve these results. My first guess is to adjust the
> "c" parameter in the mBJ functional. After some searching through the
> routines and Libxc files, I'm still clueless on how to proceed on this
> matter.
>
> Any further suggestions will be much appreciated
>
> Thank you
> Fábio Costa
>
>
>
> ------------------------------
> *De:* users <users-bounces at lists.quantum-espresso.org> em nome de Fabio
> Costa <fabiocosta4 at hotmail.com>
> *Enviado:* segunda-feira, 14 de outubro de 2019 13:10
> *Para:* users at lists.quantum-espresso.org <users at lists.quantum-espresso.org
> >
> *Assunto:* [QE-users] On the use of the modified Becke-Johnson (TB09)
> functional
>
> Dear all
>
> I'm having some difficulties to work with the TB09 functional. After some
> reading, I found in  some old posts that this can be done by compiling QE
> with Libxc, and by adding the line 'input_dft='tb09'' in the pw.x input.
>
> When I try to use this functional, the scf calculation always ends like
> this:
>
>      total energy              =              NaN Ry     Harris-Foulkes
> estimate   =     -11.24358313 Ry     estimated scf accuracy    <
> 0.01858366 Ry     iteration # 18     ecut=   120.00 Ry     beta= 0.10
>  Davidson diagonalization with
> overlap %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>    Error in routine cdiaghg (7):     eigenvectors failed to
> converge %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
> What draws my attention is that always in the last cycle before the error
> the total energy is printed as NaN. The parameters to the calculation seem
> to be fine, as it ends smoothly without the input_dft line.
>
> By searching in the QE user guide, there is a reference to the work of E.
> Germaneau, which lead me to his paper (DOI: 10.1016/j.cpc.2013.02.020
> <http://dx.doi.org/10.1016/j.cpc.2013.02.020>), where the results of his
> implementation are presented. Even though, it is unclear to me how to use
> the functional correctly.
>
> Thanks for any assistance
> Fábio Costa
> _______________________________________________
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