These three lines determine the valence and the atomic mass and the Wigner Seitz radius for each atomic species. These lines are mainly to assure compatibility between the POTCAR file and the INCAR file. The POTCAR file also contains valence information, the ordering in the POTCAR file must be the same as in the INCAR file and POSCAR file. If incompatibilities exist VASP will stop.
The Wigner Seitz radius is optional, if it is supplied, partial spd-wavefunction characters and the local partial DOS and are evaluated (see section 5.16). For mono-atomic system RWIGS can be defined unambiguously. The sum of the volume of the spheres around all atoms must be the same as the total volume of the cell (assuming that you do not have a vacuum region within your cell). VASP will write a line
Volume of Typ 1: 98.5 %to the OUTCAR file. You should use an RWIGS which gives approximately .
For binary system there is no unambiguous way to define RWIGS. Several choices are possible, but in all cases the sum of the volumes of the spheres around all atoms must be close to the total volume of the cell (i.e the sum of the values given by VASP should be ).