The polarization and charge transfer energies, DE POL and DE CT , can be further decomposed into contributions from sp-and dorbitals using a three-step procedure. In the first step, complementary occupied-virtual orbital pair (COVP) analysis is performed on both energy components. In the second step, the weights of sp-and d-contributions are assessed for each occupied or virtual orbital localized on the metal cluster. Specifically, for the q-th fragment orbital with coefficients C q (a single column vector with the span of the metal fragment basis), the corresponding "density matrix" can be written as