First-principles study of self-trapped polarons

The polaron is a quasiparticles consisting of an electron or hole dressed by a cloud of phonons. Self-trapped polarons are found when the electron-phonon interaction is so strong that the electron is bound by the potential of the lattice distortion that it induces. Here we investigate the mechanisms of polaron formation in wide-gap insulators, using Li2O2 as a prototypical example. We study self-trapping both via direct density-functional theory (DFT) calculations and using a perturbation theory approach. We analyze the binding energy in terms of the underlying band structure and phonon dispersions, and we compare our findings with previous calculations and with classic models of self-trapped polarons. We discuss open questions in the ab initio study of polarons and possible solutions.