An orthogonal electronic state view on charge delocalization and transfer

Abstract: We present a configuration interaction (CI) framework which serves quantitative and conceptual purposes for charge delocalization and electron transfer processes in molecular systems. The electronic Hamiltonian is expressed in a basis of charge-localized determinants and used to independently generate adiabatic CI states and charge-localized CI states, both of which are unambiguously defined through a diagonalization procedure. The CI framework offers a simple interpretation of adiabatic states as resonance hybrids of different electron distributions, providing a simple picture for discussing charge-delocalization in chemical bonding. The charge-localized states serve as a convenient orthogonal representation of initial and final states in electron transfer processes, and provides an unambiguous definition of their electronic coupling. These two models enable an analysis of the water dimer hydrogen bond. We demonstrate that although the overall charge delocalization is small, the occurrence of particular ionic contributions are crucial to get the correct electronic description.