needs to be solved in the basis of two charge-localized states {Φ 1 , Φ 2 }. Here, H and S are the 2×2 matrices of the Hamiltonian and overlap, respectively, whereas c is a column vector of the linear combination coefficients. The elements S nm of the overlap matrix are given according to Eq. ( ), whereas the elements of the Hamiltonian are calculated approximately as functionals of the transition electronic densities ρ nm ( r ) = ρ α nm ( r ) + ρ β nm ( r ), scaled by the overlap S nm ,