[Wien] calculating Ionic charge

[puday at iitk.ac.in]

Dear Wien2k users
Can anyone tell me how to calculate the ionic charge for an atom inside
unitcell?
I will give you an example which is published on PRB
PHYSICAL REVIEW B 79, 054510 (2009)
They have calculated "Ionic charge" and "Bader" charge for individual
atoms in the compound "LaOFeP" which is listed bellow

------------------------------------------------
Atom      Purely Ionic charge    Bader Charge
      (using purely ionic model)
------------------------------------------------
La   =     8 (La^3+)              9.05
O    =     8 (O^2-)               7.31
Fe   =     6 (Fe^2+)              7.59
P    =     8 (P^3-)               6.05
-----------------------------------------------

I don't understand how to calculate the ionic charge using "purely ionic
model" for example 8 of La^3+ ion as listed above.
Please help me.

Regards,
Uday Bhanu Paramanik
Dept.of Physics
IIT Kanpur
India