Fig. 2. SAPT(VQE) workflow for computing intermolecular interaction energies. In the first stage the input structures for the protein and ligand are provided. Following this, the structures are typically relaxed using classical molecular dynamics and DFT and a model system of the binding site is cutout from the full structure. At this stage an active space for the protein and/or ligand can be determined. Next, a quantum algorithm like the VQE is used to determine the one- and two-particle reduced density matrices which serve as input for SAPT. The SAPT interaction energy is finally computed as a classical post-processing step. Note that only the determination of the one- and two-particle density matrices (γ and Γ respectively) should be performed on a quantum computer.