NCI orbital decomposition and critical comparison to local correlation schemes.

In this study, we introduce novel orbital decomposition approaches for analyzing non-covalent interactions (NCIs) and dispersion interaction densities (DID), termed o-NCI and o-DID, respectively. Orbital pair analyses offers an opportunity to analyse in-depth NCIs in four model dimer systems to which dispersion forces contribute to different extents: argon, methane, water and benzene-acetylene dimers. The comparative calculations reveal that intuitive interpretations based solely on nearby σ- and π-orbital interactions may overlook substantial contributions from more distant orbitals. For instance, in the benzene-acetylene dimer, interactions between π-orbitals significantly contribute to the overall dispersion energy, rivaling traditional σ bond contributions. Overall, this work establishes a comprehensive framework for understanding NCIs through the lens of orbital contributions and highlights that our interpretations must account for the intricate interplay between different interaction types. It also underlines the differences between NCI and local correlation energy decomposition, paving the way for advancements in the design and analysis of molecular systems based on NCIs.