[Pw_forum] k point convergence of dielectric properties

[Prasenjit Ghosh]

Dear Dario,

For calculation of dielectric properties you need to do integrations over
the BZ. For high symmetry lattices, a shifted k-point mesh (specially a k-pt
mesh without Gamma pt.) without the high symmetry points should be used. In
that way you have a better sampling of your BZ and hence a improvement in
the results. I also found similar improvements of convergence when I tested
for convergence of adsorption energy wrt k-point mesh.

Prasenjit.

2008/10/10 dario rocca <roccad at gmail.com>

>
> Dear Users
> I have an issue related to the convergence of the static dielectric  matrix
> using the PH code. I have performed calculations
> on bulk silicon using different k point meshes and I have obtained the
> following results:
>
> k grid              diagonal component of      number of k points in
>                          the dielectric tensor           the irreducible
> Brillouin zone
>
> 4*4*4                   23.668350065                        8
>  6 *6*6                16.297485614                       16
> 8 *8*8                  14.044830694                       29
> 10 *10*10             13.288531964                     47
> 12*12*12              13.029602882                     72
> 16 *16*16             12.908820645                    145
> 20 *20*20             12.894538380                    256
>
> k grid+ 1 1 1 shift              diagonal component of      number of k
> points in
>                                             the dielectric tensor
> the irreducible Brillouin zone
>
> 4*4*4                                      13.840844632
>                           10
> 6*6*6
> 12.997009732                           28
> 8*8*8
> 12.903849607                           60
> 10*10*10                               12.893711596
> 110
> 12*12*12                               12.892685597
> 182
> 16*16*16                               12.892482798
> 408
> 20*20*20                               12.892537346
> 770
>
> I was surprised of the improvement in the convergence due to the shift of
> the grid. I don't think this is related to the number of k points
> in the IBZ (at least not exclusively).
> I have observed a similar behavior in diamond.
> The ground state energy convergence also benefits from the shift, but the
> improvement is not so striking.
> Does someone has any hint on why the shift of the grid improves the
> calculation of the dielectric properties of silicon?
> Thanks a lot
> Dario Rocca, dept. of chemistry, UC Davis
>
>
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>


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PRASENJIT GHOSH,
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