# Why does my zincblende structure not look cubic?

The structure of my material is zincblende. So normally the structure is cubic. However, when I open the primitive cell with xcrysden it dosen't look 100% cubic. It's a little bit inclined. Also when I calculated the optical properties of my material with a primitive unit cell the components of the imaginary part along x,y and z axis aren't equal (same for the real part). And normally if the structure is cubic they should be equal. Why they aren't equal?

The parameters of the conventional cell are:

  nat = 8
ntyp = 2
/
CELL_PARAMETERS {alat}
1.000000000000000   0.000000000000000   0.000000000000000
0.000000000000000   1.000000000000000   0.000000000000000
0.000000000000000   0.000000000000000   1.000000000000000


For the primitive cell the parameters are:

  nat = 2
ntyp = 2
/
CELL_PARAMETERS {alat}
0.500000000000000   0.500000000000000   0.000000000000000
0.500000000000000   0.000000000000000   0.500000000000000
0.000000000000000   0.500000000000000   0.500000000000000


a visualization of primitive cell using xcrysden

• Primitive unit cell and conventional unit cells of any crystal structure are NOT necessarily the same. In your case, this is evident from the lattice parameters you provided.
– Sha
Commented Mar 27, 2023 at 14:11
• @Sha I know that it can be seen from the lattice parameters however the structure is cubic so for the optical components for example they should be the same along x, y and z axis, am I right? Commented Mar 27, 2023 at 14:16
• What do you mean by the structure is cubic? Did you simulate the primitive cell or the conventional unit cell? What are your input parameters of the simulated structure?
– Sha
Commented Mar 27, 2023 at 15:51
• @Sha my simulated structure is primitive Commented Mar 27, 2023 at 23:12
• Then there is nothing wrong with your simulation output, as is well elaborated by @Abdul's answer.
– Sha
Commented Mar 28, 2023 at 0:53

Edit: If you want to see the cubic conventional cell structure using XCrySDen, then press F4 key or select conventional cell mode from the Display menu.