Many-Body Expanded Full Configuration Interaction: II. Strongly Correlated Regime

TLDR: This second part of the series on the recently proposed many-body expanded full configuration interaction (MBE-FCI) method introduces the concept of multideterminantal expansion references and shows a focussed compression of the MBE decomposition of the FCI energy, allowing chemical problems dominated by strong correlation to be addressed by the method.

Abstract: Over the course of the past few decades, the field of computational chemistry has managed to manifest itself as a key complement to more traditional lab-oriented chemistry. This is particularly true in the wake of the recent renaissance of full configuration interaction (FCI)-level methodologies, albeit only if these can prove themselves sufficiently robust and versatile to be routinely applied to a variety of chemical problems of interest. In the present series of works, performance and feature enhancements of one such avenue toward FCI-level results for medium to large one-electron basis sets, the recently introduced many-body expanded full configuration interaction (MBE-FCI) formalism [ J. Phys. Chem. Lett. 2017, 8, 4633], will be presented. Specifically, in this opening part of the series, the capabilities of the MBE-FCI method in producing near-exact ground state energies for weakly correlated molecules of any spin multiplicity will be demonstrated.