[QE-users] External parameters for libxc functionals

[Fabrizio Ferrari]

Hello,
the message simply means that the chosen functional depends on a number of
parameters that can be 'manually' set by the user, otherwise their default
value is kept. As far as I could see the external dependence on parameters
in SCAN has been introduced in the last releases of libxc (v5.0.0 and
5.1.0). In the preceding versions they were fixed.
Below the output of a XC-info program that will be available in the next
release of QE and that provides infos on the libxc functionals (you can try
it in the develop version)
----------------------------------------------------------------------------------
SCAN = mgga_x_scan (263) + mgga_c_scan (267)

Functional with ID:         263
The functional 'SCAN exchange of Sun, Ruzsinszky, and Perdew' is an Exchange
functional, it belongs to the 'MGGA' family and is defined in the
reference(s):
[1] J. Sun, A. Ruzsinszky, and J. P. Perdew, Phys. Rev. Lett. 115, 036402
(2015)

 Number of external parameters:            4
 c1 parameter
 Default value:   0.66700000000000004
 c2 parameter
 Default value:   0.80000000000000004
 d parameter
 Default value:    1.2400000000000000
 k1 parameter
 Default value:    6.5000000000000002E-002

Functional with ID:         267
The functional 'SCAN correlation of Sun, Ruzsinszky, and Perdew' is a
Correlation functional, it belongs to the 'MGGA' family and is defined in
the reference(s):
[1] J. Sun, A. Ruzsinszky, and J. P. Perdew, Phys. Rev. Lett. 115, 036402
(2015)
 Number of external parameters:            0
---------------------------------------------------------------------------------------
In the next release of QE there will be two routines that can be called
anywhere in the code to set libxc parameters or to recover their default
values (file dft_mod.f90 in XClib). If you need to act on the source code
to change some libxc parameters you can have a look there in the develop
branch of QE.
Cheers,
Fabrizio

On Tue, Feb 9, 2021 at 9:28 PM Hien Vo <hvo at uchicago.edu> wrote:

> Hello,
>
>
>
> I recently tried to perform scan calculations on qe6.6 compiled with
> libxc-5.1 via including
>
>
>
> Input_dft=’scan’
>
>
>
> In the input. I got the following warning:
>
>
>
>      WARNING: one or more of the chosen libxc functionals depend
>
>       on external parameters: their correct operation is not guaranteed.
>
>
>
> How do I fix this? The user manual for QE says that I might have to fix
> the source code by entering in the parameters but I don’t know what they
> are …
>
>
>
> Best,
>
>
>
> Hien Vo <https://galligroup.uchicago.edu/People/hvo.php>
>
> PhD Candidate
>
> Chemistry Department | The University of Chicago
>
>
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