Energy decomposition analysis (EDA) aims to quantitatively bridge the gap between quantum chemistry calculations and chemical intuition by providing values for the chemical drivers of intermolecular interactions, such as permanent electro- statics, Pauli repulsion, dispersion, and charge transfer. The goal is similar for chemical bonding, where one must also carefully account for bond formation via spin-coupling. These energetic contributions are identified by performing DFT calculations with constraints that disable components of the interaction. The second generation version of the absolutely localized molecular orbital EDA (ALMO- EDA-II) will be described. The effect of different physical contributions on changes in observables such as structure, vibrational frequencies etc, upon complex formation is achieved via the adiabatic EDA. A variety of chemical examples will be presented to illustrate the usefulness of this approach, including bonding and frequency shifts of CO, N2, and BF bound to a [Ru(II)(NH3)5]2+ moiety, and the nature of the strongly bound complexes between pyridine and the benzene and naphthalene radical cations. The origin of the chemical bond will also be discussed, as will a few of the other controversies concerning the character of chemical interactions.
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Financial Support
The Cooper Union for the Advancement of Science and Art is pleased to provide support for the 2024 VWSCC through a generous donation from Alan Fortier.
We thank Leibniz Institute for Catalysis (LIKAT) and CECAM for their support.
Virtual Winter School on Computational Chemistry