[Pw_forum] Gipaw - Magnetic susceptibility

[Davide Ceresoli]

Dear Alan,
     I think that there is no problem in doing a G=0 response
with a shifted mesh. The response is at G=0, hence it couples
wfcs at the same k. The susceptibility depends a lot on k-points
sampling and if your system has a vanishing band gap, convergence
can be a nightmare.
By default the macroscopic shape is diagonal:
   nmr_macroscopic_shape(:,:) = 0.d0
   nmr_macroscopic_shape(1,1) = 2.d0 / 3.d0
   nmr_macroscopic_shape(2,2) = 2.d0 / 3.d0
   nmr_macroscopic_shape(3,3) = 2.d0 / 3.d0
You can change the component (demagnetizing field) in the input file.

Good luck for your calculations!

Best,
     Davide



On 05/12/2017 07:47 PM, Ambrozio wrote:
> Dear QE users and Developers,
>
> I'm working with NMR calculations in Gipaw. Recently I did some shielding
> calculations and I have some questions regarding the magnetic susceptibility.
> The article from developers Mauri et al (*PRL 77, 26, 1996*) explain that the
> shielding of a bulk of a periodic system is also periodic (i.e. has the same
> periodicity of *G*, the reciprocal lattice vectors), and it is proportional to
> the magnetic susceptibility matrix. In the paper Mauri did a short discussion
> about the macroscopic susceptibility, which is calculated at *G=0*. Follow my
> questions:
>
> i) Assuming that the macroscopic susceptibility is calculating at gamma point
> (*G=0*) and depends of the sample's shape, Does make sense to do a NMR
> calculation with automatic kpoints (monkhorst pack grid)  that does not include
> the gamma point? It is mandatory to including the gamma point when the shape
> correction is .true.?
>
> ii) Does the susceptibility depends of the supercell size? I found very
> different susceptibilities for the same material (AB graphite) changing the
> supercell size.
>
> iii) Why the susceptibility  matrix is not diagonal when the shape correction is
> .true.? Assuming the Mauri paper I think it doens't make sense. Help me to
> understand...
>
>
> I appreciate any help,
>
> Thanks in advance,
>
>
> Alan.
>
>
>
> --
>
> Alan J. Romanel Ambrozio
> Bacharel em Física
> Mestre em Eng. de Materiais
> Doutorando em Física - PPGFis
>
>
>

-- 
+--------------------------------------------------------------+
   Davide Ceresoli
   CNR Institute of Molecular Science and Technology (CNR-ISTM)
   c/o University of Milan, via Golgi 19, 20133 Milan, Italy
   Email: davide.ceresoli at cnr.it
   Phone: +39-02-50314276, +39-347-1001570 (mobile)
   Skype: dceresoli
   Website: http://sites.google.com/site/dceresoli/
+--------------------------------------------------------------+