A note about symmetry

The fact that the point group operations are rigidly related to the Cartesian axes, the symmetry determined by tetr may not be as rich as it should be. On the other hand, in many cases it is useful to have the maximum symmetry possible (e.g. when generating $\mathbf{k}$-points for the electronic DOS calculation). Therefore, it is advised to maximise the system symmetry by shifting and/or rotating the whole cell. This can be done in the M-menu, Section 2.6.5, where each time you change your system, the symmetry group is recalculated so that you can check the symmetry at every stage (option Sy).

In order to do a band-structure calculation, you should first relax your system and obtain the electronic density. Note that the ground state density can be left unchanged if you just rotate your coordinate system (we assume that it is written with respect to the fractional coordinates of the grid points in your cell; this supposed to be the case in both VASP and SIESTA). However, if you have to shift your system by some vector, then the density matrix should be recalculated and a new file must be produced. This option is provided by the utility lev00 (see Section 3.6.3.13). Therefore, it is always wise to think about it before running the ground state calculation: choose the most symmetrical orientation of the system with respect to the Cartesian axes, use tetr to show the point group every time!