A Non-Perturbative Pairwise-Additive Analysis of Charge Transfer Contributions to Intermolecular Interaction Energies

TL;DR

This paper introduces a numerically exact, non-perturbative method for decomposing charge transfer energies into pairwise contributions within the ALMO-EDA framework, applicable to strongly interacting systems and revealing new insights.

Contribution

A novel, exact pairwise decomposition scheme for charge transfer energies in ALMO-EDA that overcomes limitations of perturbative methods and is applicable to complex systems.

Findings

Decomposition works for strongly interacting systems.

Provides insights into donor-acceptor interaction trends.

Applicable to diverse molecular systems.

Abstract

Energy decomposition analysis (EDA) based on absolutely localized molecular orbitals (ALMOs) decomposes the interaction energy between molecules into physically interpretable components like geometry distortion, frozen interactions, polarization, and charge transfer (CT, also sometimes called charge delocalization) interactions. In this work, a numerically exact scheme to decompose the CT interaction energy into pairwise additive terms is introduced for the ALMO-EDA using density functional theory. Unlike perturbative pairwise charge-decomposition analysis, the new approach does not break down for strongly interacting systems, or show significant exchange-correlation functional dependence in the decomposed energy components. Both the energy lowering and the charge flow associated with CT can be decomposed. Complementary occupied-virtual orbital pairs (COVPs) that capture the dominant donor and acceptor CT orbitals are obtained for the new decomposition. It is applied to systems with different types of interactions including DNA base-pairs, borane-ammonia adducts, and transition metal hexacarbonyls. While consistent with most existing understanding of the nature of CT in these systems, the results also reveal some new insights into the origin of trends in donor-acceptor interactions.