Hi Everyone, we will be hosting Johnathan Thirman on Thursday. His talk will be in the Division Room from 11am-12pm. The title and abstract are below. Best Christoph An energy decomposition analysis for second-order Møller–Plesset perturbation theory based on absolutely localized molecular orbitals Intermolecular interactions control the properties and behaviors of a wide variety of systems. Intuitively, the forces between molecules can be divided into several different categories, such as London dispersion force, induced dipole forces, permanent dipole forces, and covalent-type interactions, each with their own characteristic strengths, properties, and decay rates. The standard supermolecule approach gives accurate binding energies, but combines all different intermolecular interactions into a single number. Energy decomposition analysis (EDA) methods exist to divide the total binding energy into its physically meaningful components. However, there has been limited development of EDAs for second-order Møller--Plesset perturbation theory (MP2), despite its utility for intermolecular interactions. An energy decomposition analysis of intermolecular interactions is proposed for MP2 based on absolutely localized molecular orbitals (ALMOs), as an extension to a previous ALMO-based EDA for self-consistent field methods. It is based on dividing the double excitations that contribute to the MP2 wave function into classes based on how the excitations involve different molecules. The MP2 contribution to the binding energy is decomposed into four components: frozen electrostatic interaction, polarization, charge transfer, and dispersion. Charge transfer is defined by excitations that change the number of electrons on a molecule, dispersion by intermolecular excitations that do not transfer charge, and polarization and frozen electrostatics by intra-molecular excitations. The final two are separated by evaluations of the frozen, isolated wave functions in the presence of the other molecules, with adjustments for orbital response. Unlike previous EDAs for electron correlation methods, this one includes components for the electrostatics, which is vital as adjustment to the electrostatic behavior of the system is in some cases the dominant effect of the treatment of electron correlation. In fact, these effects may be strong enough to make the overall effect of correlation anti-binding.