Time- and charge-dependent atom-atom potentials for vibronic coupling in nonequilibrium electronic states

In an attempt to characterize vibronic effects in anharmonic solids, an approach to electron-vibrational coupling is developed that is not based on an expansion, in atomic displacements, of the electron-nuclei interaction. This approach avoids the linear and quadratic coupling limitations of standard polaron models. It uses experimentally known (or calculated by quantum chemistry methods) potentials for clusters of atoms in different ionic states of the cluster, and explores the idea of potentials at fractional electron densities. The advantages of the approach are illustrated for the case of strong coupling in anharmonic situations, where the expansion approaches fail.