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Energy Decomposition Analysis for Interactions of Radicals: Theory and Implementation at the MP2 Level with Application to Hydration of Halogenated Benzene Cations and Complexes between CO2-· and Pyridine and Imidazole.

  • Author(s): Loipersberger, Matthias
  • Lee, Joonho
  • Mao, Yuezhi
  • Das, Akshaya K
  • Ikeda, Kevin
  • Thirman, Jonathan
  • Head-Gordon, Teresa
  • Head-Gordon, Martin
  • et al.
Abstract

To study intermolecular interactions involving radicals at the correlated level, the energy decomposition analysis scheme for second-order Mo̷ller-Plesset perturbation theory based on absolutely localized molecular orbitals (ALMO-MP2-EDA) is generalized to unrestricted and restricted open-shell MP2. The benefit of restricted open-shell MP2 is that it can provide accurate binding energies for radical complexes where density functional theory can be error-prone due to delocalization errors. As a model application, the open-shell ALMO-MP2-EDA is applied to study the first solvation step of halogenated benzene radical cations, where both halogen- and hydrogen-bonded isomers are possible. We determine that the lighter halogens favor the hydrogen-bonded form, while the iodine-substituted species prefers halogen bonding due to larger polarizability and charge transfer at the halogen. As a second application, relevant to the activation of CO2 in photoelectrocatalysis, complexes of CO2-· interacting with both pyridine and imidazole are analyzed with ALMO-MP2-EDA. The results reveal the importance of charge transfer into the π* orbital of the heterocycle in controlling the stability of the carbamate binding mode, which is favored for pyridine but not for imidazole.

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