where ∆E SCS-CIS(D) is the SCS-CIS(D) excitation energy. This means there is a direct mapping between the scale parameters of the indirect term and the ground-state energy expression. When neglecting the SS component, one arrives at the SOS versions of CIS(D) and MP2, but the same mapping between ground-state method and indirect term can be established. The total energy of the SOS-CIS(D) excited state is then simply the sum of the SOS-MP2 ground-state energy and the SOS-CIS(D) excitation energy. These connections will be crucial for the definition of the ground-state energy of the double hybrid density functionals introduced in the following section.