Quantum Equation of Motion in Active Spaces for Computing Molecular Excitation Energies in Near-Term Quantum Computing

Determining the properties of molecules and materials is one of the premier applications of quantum computing. A major question in the field is: how might we use imperfect near-term quantum computers to solve problems of practical value? Inspired by the recently developed variants of the quantum counterpart of equation-of-motion (qEOM) approach and the orbital optimized variational quantum eigensolver (oo-VQE), we present a quantum algorithm for the calculation of molecular excitation energies and excited states using the active space approximation.