As we treat the spins independently, two sets of determinants, Λ ↑ , Λ ↓ , describe the full configuration, for CI states I, and occupied MOs i (in general for open-shell cases Λ ↑ and Λ ↓ may have different amount of occupied orbitals. Also within each spin-type each determinant may have different amount of occupied orbitals, i.e. Spin-Flip):