Partitioning dynamic electron correlation energy: Viewing Møller-Plesset correlation energies through Interacting Quantum Atom (IQA) energy partitioning

Highlights: • This is the first instance of a full IQA partitioning of a Møller-Plesset perturbation theory wave function. • A new avenue for deriving DFT dispersion corrections free of damping functions. • Rigorous tool to quantify intra-atomic dispersion and explore its relationship to the intra-atomic contributions. • Pivotal extension to the FFLUX force field. Here MP2, MP3 and MP4(SDQ) are energy-partitioned for the first time within the Interacting Quantum Atoms (IQA) context, as proof-of-concept for H₂, He₂ and HF. Energies are decomposed into four primary energy contributions: (i) atomic self-energies, and atomic interaction energies comprising of (ii) Coulomb, (iii) exchange and (iv) dynamic election correlation terms. We generate and partition one- and two-particle density-matrices to obtain all atomic energy components. This work suggests that, in terms of Van der Waals dispersion, the correlation energies represent an atomic stabilisation, by proximity to other atoms, as opposed to direct interactions with other nearby atoms.