Home
The Regular Point System (RPS) codes encodes the
symmetry elements generated by the space-group. The description of the crystal
structure can be simplified when it contains only atoms located at high symmetry
positions. For Silicon (F d-3m space-group)
the majority of the generated codes is redundant since the Si atom has (x = 0,
y = 0, z = 0) coordinates. The Silicon crystal structure requires only two RPS codes:
(x, y, z) and (x + 1/4, y + 1/ 4, z + 1/4) together with a F Bravais lattice.
Figure 1 Silicon Regular
Point System code.
To describe the Si symmetries modify the codes generated by F d3m (Fig. 2) with
the RPS code Editor.
Suppress all RPS codes.
Add RPS code.
 |
 |
Figure 2a RPS code editor. |
Figure 2b RPS code
(x + 1/4, y + 1/4, z + 1/4). |
The 
delete the selected code.
Check the Face Centering radio button and set the lattice parameter.
It suffices now to place one Si atom at (0, 0, 0) to generate the conventional
Silicon crystal structure (Fig. 3a).
 |
 |
Figure 3a Si at (0,0,0). |
Figure 3b Si structure. |
The description of ZnTe structure is even simpler since only RPS code (x, y, z) and F Bravais lattice.
The tabular list of the RPS code is given in Figures 4a, 4b,
4c.
ZnTe only requires one Zn atom at (0, 0, 0) and one Te atom at (1/4, 1/4, 1/4) (Fig. 5).
 |
 |
 |
Figure 4a General positions. |
Figure 4b Special positions. |
Figure 4c Point group. |
 |
 |
Figure 5a Zn at (0,0,0)
Te at (1/4, 1/4, 1/4). |
Figure 5b ZnTe structure. |
Using this description of ZnTe can produce a large speed up of some crystallographic
calculations.