  In this paper, we scrutinize the ability of seniority-zero wavefunction-based
methods to model different types of non-covalent interactions, such as hydrogen
bonds, dispersion, and mixed non-covalent interactions as well as prototypical
model systems with various contributions of dynamic and static electron
correlation effects. Specifically, we focus on the pair Coupled-Cluster Doubles
(pCCD) ansatz combined with two different flavours of dynamic energy
corrections, (i) based on a perturbation theory correction and (ii) on a
linearized coupled-cluster ansatz on top of pCCD. We benchmark these approaches
against the A24 data set [\v{R}ez{\'{a}}{\v{c}} and Hobza,
J.~Chem.~Theory~Comput., 9, 2151-2155 (2013)] extrapolated to the basis set
limit and some model non-covalent complexes that feature covalent bond
breaking. By dissecting different types of interactions in the A24 data set
within the Symmetry-Adapted Perturbation Theory (SAPT) framework, we
demonstrate that pCCD can be classified as a dispersion-free method.
Furthermore, we found that both flavours of post-pCCD approaches represent
encouraging and computationally more efficient alternatives to standard
electronic structure methods to model weakly-bound systems, resulting in small
statistical errors. Finally, a linearized coupled cluster correction on top of
pCCD proved to be most reliable for the majority of investigated systems,
featuring smaller non-parallelity errors compared to perturbation-theory-based
approaches.
