# How to construct spin free coefficient of 2-hole 1-particle configuration?

It is clear that we can expand a cationic state of a molecule in terms of configuration interaction (up to double excitation). It means: $$|I \rangle = \sum_j c^{(I)}_j a_j|\phi_0 \rangle \ + \ \sum_{r,k

where C are coefficients, $$a_i(a^{\dagger})$$ is annihilation (creation) operator, and $$|\phi_0 \rangle$$ is HF Ground state of nuetral molecule.

I would like to know how can I construct spin-free $$c^{(I)}_{rkl}$$, which is the coefficient of 2h1p configuration? Particularly, I interested in this procedure when cationic state and accordingly 2h1p configuration is doublet.