The electronic energy, E_{r}, of any microstate
Ψ_{r }is the sum on the one and two-electron energies:

where H_{ii} is the one-electron energy of M.O.
ψ_{i}, J_{ii} is the two-electron Coulomb integral
<ψ_{i}ψ_{i|}ψ_{j}ψ_{j>}, and K_{ii} is the two-electron exchange integral
<ψ_{i}ψ_{j|}ψ_{i}ψ_{j>}. In this section it is more convenient to express it in terms of molecular orbital occupancies: