Events

Date: 4 March 2026   Time: 15:00 - 16:00

Location: GO Jones 610

Title: Symmetry-Adapted Relaxation Theory (SART): Exact theory of embedding and a new way of calculating interaction energies with infinite-order induction relaxation of the monomers

Speaker: Dr Alston Misquitta (QMUL)

Abstract: Symmetry-adapted perturbation theory (SAPT), in its many flavours, remains the foundation of much of our understanding of intermolecular interaction energies. This is not only because of the high accuracies of SAPT-like theories (SAPT2, SAPT2+3, SAPT(DFT), SAPT(CCSD), SAPT(MC), etc.), but also because of the physical interpretation of the interaction energy and the well-defined asymptotic expansions for each of the non-exchange terms in SAPT approaches. However, none of the SAPT methods are true perturbation theories as all rely on a post-, non-perturbative correction to account for missing higher-order induction terms. Further, SAPT has been formulated as few-body theory: only two-body, and three-body interactions are included.
Here we propose a new foundation for a SAPT-like formalism that is based on the variational principle, and the non-orthogonal relaxation of monomer wavefunctions in the electrostatic and exchange potentials of the partners. This theory, termed symmetry adapted relaxation theory (SART), is first and foremost, an exact method for embedding, but it also obtains the induction interaction of the monomers to infinite-order in the interaction operator and thus provides us with a unique and powerful formalism for a SAPT-like theory.
I will demonstrate the current status of SART[HF] and demonstrate how the formalism allows us to obtain interaction energies, and observables like the monomer densities with interaction-induced changes.