The computational protocol exploits the existing infrastructure of OpenMolcas as much as possible, as displayed in Fig. , demonstrating the general computational workflow. An input example is given in the Supporting Information. The computation of the two-electron integrals involving AOs of both monomers and their Cholesky decomposition is performed only once in section (a) of the input. In this section, the monomer m is denoted as a dummy fragment for the (fake) calculation of the BSSE correction (keyword bsse = 1). In addition, the matrix elements of the electron-nuclear potential V m γδ are computed. In section (b) of the input, the required V n αβ integrals are computed; for this, the monomer n is denoted as a dummy fragment (bsse = 2). Via the fake ricd directive one avoids recomputing twoelectron integrals and their Cholesky decomposition, as it has already been done at step (a). The information on the integrals and their decomposition is stored in two "RunFiles": Finally, all ingredients come together in the RASSI calculation (e) containing the keywords MONB and EXCI. The first one triggers the calculation of the missing intermediates