Reduced‐scaling coupled cluster response theory: Challenges and opportunities

We review the current state of reduced‐scaling electron correlation methods, particularly coupled‐cluster theory for the simulation and prediction of molecular response properties. The successes of local‐coupled‐cluster and related approaches are well known for reaction energies, thermodynamic constants, dipole moments, and so forth—properties that depend primarily on the quality of the ground‐state wave function. However, much more challenging are higher‐order properties such as polarizabilities, hyperpolarizabilities, optical rotations, magnetizabilities, and others that also require accurate representation of the derivative of the wave function to external electromagnetic fields. We discuss a range of methods for improving the correlation domains of such perturbed wave functions, including the use of “perturbation‐aware” natural orbitals that are customized for the property of interest. In addition, we consider the viability and potential of promising, but still‐emerging methods such as stochastic and real‐time coupled‐cluster approaches, for which the localizability of the field‐dependent wave function may be more controllable than for conventional response theory. This article is categorized under: Electronic Structure Theory > Ab Initio Electronic Structure Methods Theoretical and Physical Chemistry > Spectroscopy Software > Quantum Chemistry We review current and emerging methods for reducing the high‐degree polynomial scaling of coupled cluster response theory.