Interaction Energies on Fault-Tolerant Quantum Computers

The efficient computation of the ab initio interaction energy between a dimer of noncovalently-bound molecular monomers is a crucial quantity in pharmacology, as it provides a path to model the binding strength between proposed drug-ligand and target-protein pairs. Classical electronic structure calculations can determine the interaction energy as a direct observable in energy decomposition analysis methods such as symmetry-adapted perturbation theory (SAPT). Here, we describe the design of a tangible quantum algorithm for computing the intermolecular interaction energy with SAPT for fault-tolerant quantum computers. The algorithm determines the energy by estimating the expectation value of the SAPT operator. We assess the necessary qubit resources, required circuit depth, expected accuracy, and specific steps needed to implement such an algorithm down to the gate level.