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

[Chengyang Li]

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,