Spinors's Symmetry File

The symmetry files that Spinor uses are based on the concept of spin space groups (SSGs). Conventionally the files end with '.ssg'. There are four blocks in each SSG file. First comes a list of spatial rotation matrices, then a list of spatial translation vectors for non-symmorphic groups, followed by a list of allowed SSG operations. Each of these lists starts with the number of elements in the list, followed by the elements (matrices, vectors or index vectors). Finally a flag indicates whether inversion shall be included in the k-point set reduction. This flag is convenient for certain symmetries if the chemical lattice and the spin are decoupled (no spin-orbit coupling present).

Spinor uses the symmetry operations listed in the SSG file to reduce the given k-point grid of the Brillouin zone and to symmetrize the electron density and spin polarization. For convenience here are some common symmetry files. The name convention is such that a single Schönflies label corresponds to the case where spin and lattice are decoupled, a double Schönflies label indicates Shubnikov groups.

• Cubic groups:
  • Oh.ssg
  • Td.ssg
  
  
• Tetragonal groups:
  • D4h-C4h.ssg
  
  

Note: The k-point grid is determined in the [Kpoints] section of the Spinor parameter file. It is either given in grid format (grid nx ny ny) or in form of a file (file filename). The k-point file has the following format:

number of k-points in file
x, y, z, weight of 1st k-point
x, y, z, weight of 2nd k-point
.
.
x, y, z, weight of last k-point

As an example you can take a look at ZB.L.G.X.UK.G.35.kpts which provides the k-points along the high symmetry lines in the Brillouin zone for zincblende materials.

If the [Symmetry] key block is present in the parameter file and the reducekpts flag is active, then the given k-point set will be reduced according to the symmetry operations listed in the symmetry file.