Core/shell

Hello dear users and developers!
Help me understand. Don’t judge me, I am novice user. I am going to use core-shell model in Cromacs. If I understand correctly, the harmonic force constant k(cs) is computed by equation: k(cs) = q(s)^2 / a, polarizability a can be calculated by ab-initio methods or given by experiments. How can the charge on the shell particle q(s) be obtained?

Best regards,
Bogdan