, where |𝑗⟩ ∈ 𝑉 𝑆𝐷 . |𝑗⟩ can be represented using excitation operators as 𝐸 ̂𝑝𝑞 𝐸 ̂𝑟𝑠 |0⟩, where p, q, r, and s belong to one of the orbital spaces, namely the inactive, active, or secondary space, selected such that the state |𝑗⟩ does not belong to 𝑉 𝐾 . The coefficients 𝐶 𝑗 necessary for the calculation of 𝐸 2 can be determined by solving the following linear equation: