Is there any mathematical formula for electron affinity and ionization potential?

I already know about the mathematical formula for electronegativity, but it requires the ionization potential and electron affinity. How can I can easily calculate the ionization potential and electron affinity with a mathematical formula?

• You can't.$\mathstrut$ – Ivan Neretin Oct 17 '17 at 16:46
• Technically, you could solve the multi-electron Schrodinger equation and compute the energy difference, but I believe that is an intractable problem without at least severe approximations. – Zhe Oct 17 '17 at 17:01
• @Zhe one such severe approximation is to solve the Schrodinger equation using the Hartree Fock approximation, then assume frozen orbitals for the ionization process. en.wikipedia.org/wiki/Koopmans'_theorem – Tyberius Oct 17 '17 at 17:07