electroncoupling

Electron coupling, often called electronic coupling, refers to the interaction that enables electronic states to influence each other across distance or between different parts of a system. It is a key ingredient in processes where charge is transferred or transported, including molecular electron transfer, exciton migration in organic materials, and charge carrier motion in solids. The concept is used across chemistry, physics, and materials science, with related notions such as electron-phonon coupling describing interactions between electrons and lattice vibrations.

In chemistry, electronic coupling is quantified by a coupling matrix element Hab between donor and acceptor states. It governs the rate of electron transfer together with the reorganization energy and the driving force, as described in Marcus theory. In the weak-coupling (nonadiabatic) regime the rate scales with Hab squared; in the strong-coupling (adiabatic) regime the electronic states mix into a single potential energy surface and transfer follows that surface. Electronic coupling also underpins photoinduced charge separation and intersystem crossing in photoactive molecules.

In condensed matter physics, electron-phonon coupling describes the interaction between electrons and lattice vibrations. It influences electrical resistance, mobility, and, at sufficiently strong strength, superconductivity via Cooper pair formation. The coupling strength is often summarized by a dimensionless parameter lambda or by the Eliashberg spectral function α^2F(ω). Theoretical models include the Froehlich and Holstein pictures, while experiments such as angle-resolved photoemission spectroscopy probe the interactions.

Computational and experimental approaches are used to quantify electron coupling. Methods include constrained density functional theory, time-dependent DFT, many-body perturbation theory, and density functional perturbation theory; experiments employ spectroscopy, Raman scattering, ARPES, and transport measurements to characterize coupling and its consequences.