Mesh and Tetrahedra

It now remains to construct a mesh in the irreducible wedge of the Brillouin zone and define the corresponding tetrahedra. This is done in the subroutine TGEN, and we shall briefly illustrate the procedure with the example of a simple cubic lattice. 

The irreducible wedge of the Brillouin zone of the simple cubic structure 

The subroutine TGEN constructs the mesh and establishes the mesh-point numbers N1.N7 for the seven neighbours of a given point. Some of these numbers are zero in special cases, e.g. Fig.9.3b where N6 = N7 = 0. It is 

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