[Pw_forum] problems of the K points of the unit cell and supercell

[Yun Wang]

Hi Chengyang,

   You can run a series of calculations with different k-point meshes. The
right k-point mesh density can be determined once the total energies
converge.

Cheers,
Yun


On Thu, Apr 25, 2013 at 5:18 AM, Chengyang Li <li.chengyang at wmich.edu>wrote:

> Dear all
>
>      I have a question about the K points. When I try to repeat the unit
> cell to get a supercell. I found someone said if the structure is changed,
> the K points should be changed at the same time if we want to keep the same
> result. I try to calculate the phonon of the chromium, the atomic positions
> and cell parameters are like this:
>
> Unit cell
>
> ATOMIC_POSITIONS crystal
> Cr1      0.000000000   0.000000000   0.000000000
>
>
> CELL_PARAMETERS cubic
>    0.500000000   0.500000000   0.500000000
>   -0.500000000   0.500000000   0.500000000
>   -0.500000000  -0.500000000   0.500000000
>
> Supercell, there are two unit cells in this cell.
>
> ATOMIC_POSITIONS crystal
> Cr1      0.000000000   0.000000000   0.000000000
> Cr1      0.000000000   0.000000000   0.500000000
> Cr1      0.500000000   0.500000000   0.250000000
> Cr1      0.500000000   0.500000000   0.750000000
>
> CELL_PARAMETERS
>    1.000000000   0.000000000   0.000000000
>    0.000000000   1.000000000   0.000000000
>    0.000000000   0.000000000   2.000000000
>
> If I set the unit cell like this
>
> K_POINTS automatic
>   4 4 4 1 1 1
>
> How should I change the k points in the supercell?
>
>
> Thank you for the attention.
>
> Chengyang Li
>
> Western Michigan University,
>
>
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>



-- 

Dr. Yun Wang
Research Fellow
Centre for Clean Environment and Energy
Griffith School of Environment
Gold Coast Campus, Griffith University
QLD 4222, Australia
Tel:(61-7) 5552 8456
Fax:(61-7) 5552 8067
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