How can the electrostatic potential between two ions be calculated?

Hello everyone:

Recently, I have been calculating the electrostatic potential of the PEDOT:PSS molecule. However, this molecule is composed of two ions. Furthermore, the PEDOT ions and the PSS ions carry charges, respectively, and PEDOT as a whole carries a positive charge.

So, how should I distribute the charges and how do I calculate it?

Looking forward to your replys

Best regards

Yi Mu