RWIGS

The Wigner Seitz radius is optional. It must be supplied for each species in the POSCAR file i.e.

 RWIGS = 1.0 1.5

for a system with 2 species (types of atoms). If the RWIGS values is supplied, the spd- and site projected wave function character of each band is evaluted, and the local partial DOS is calculated (see sections 5.16 and 5.15). For mono-atomic system RWIGS can be defined unambiguously. The sum of the volume of the spheres around each atom should be the same as the total volume of the cell (assuming that you do not have a vacuum region within your cell). This is in the spirit of atomic sphere calculations. VASP writes a line

 Volume of Typ   1:     98.5 %

to the OUTCAR file. You should use a RWIGS value which yields a volume of approximately $100\%$.

For binary system there is no unambiguous way to define RWIGS and several choices are possible. In all cases, the sum of the volume of the spheres should be close to the total volume of the cell (i.e the sum of the values given by VASP should be around $100\%$).

• One possible choice is to set RWIGS so that the overlap between the spheres is minimized.
• However in most cases, it is simpler to choose the radius of each sphere so that they are close to the covalent radius as tabulated in most periodic tables. This simple criterion can be used in most cases, and it relies at least on some ``physical intuition''.

Please keep in mind that results are qualitative -- i.e. there is no unambiguous way to determine the location of an electron. With the current implementation, it is for instance hardly possible to determine charge transfer. What can be derived from the partial DOS is the typical character of a peak in a DOS. Quantitative results can be obtained only by carefull comparison with a reference system (e.g. bulk versus surface).