Calcite (CaCO3 )
6. With Lt we can now select the translational vectors
7. Here, we show how to build the calcite unit cell using the rhombohedral representation. For this, enter 1.
8.
In the rhombohedral unit cell, the translational vectors a1, a2 and a3 are of equal length a.
For calcite and the angle between the
vectors
Once you specify these 2 parameters, tetr builds the three lattice vectors and shows you the list of symmetry operations belonging to the D3d space group.
9. Use Su to choose the conventional cell which requires the unit matrix 100, 010 and 001 as an extension.
10. Finally, we can add the atomic positions for Ca, C and O respectively.
tetr gives you the option to insert manually the atomic species and their coordinates (command At ) or you can read the data from a file (command Ad).
}
Note that according to option Ca (see under the “general settings”) atoms are to be specified in fractional coordinates with respect to the conventional unit cell. In our case this one is the same as the primitive one.
