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.