UC Berkeley

In this thesis, a newly developed second-generation energy decomposition analysis (EDA)based on second order Møller-Plesset perturbation theory (MP2) is presented. EDA’s have become widely used to aid in understanding the nature of intermolecular interactions and are commonly based on density functional theory (DFT) and self-consistent field (SCF) calculations. However, using correlated post-SCF methods, such as MP2, for EDA is less common, partly due to the complexity associated with defining suitable approaches. As such, this thesis focuses on presenting a new approach for EDA’s for post-SCF methods through the implementation of restricted and unrestricted MP2 EDA calculations. This newly developed MP2 EDA builds upon the SCF-level second-generation absolutely localized molecular orbital EDA approach (ALMO-EDA-II) and provides distinct energy contributions for a frozen interaction energy (containing permanent electrostatics and Pauli repulsions), a polarized energy (yielding induced electrostatics), a dispersion-corrected energy, and the fully relaxed energy (which yields charge transfer). Importantly, the theory has been designed such that there are stable basis set limits for each term, evidenced by basis set stability calculations on a wide variety of systems as well as the S22 and Ionic43 datasets. Additionally, MP2 ALMO-EDA-II has been applied to four non-covalently bonded classes of complexes; a class of conventional hydrogen bonded systems, a class of non-conventionally hydrogen bonded systems, a class of tetrel bonded systems, and a “solvent-resistant” halogen bonded system. Through these systems, the usefulness of MP2 ALMO-EDA-II is explored, especially through its treatment of the correlation component of the interaction energy.