Spontaneous charge carrier localization in extended one-dimensional systems

TL;DR

This paper demonstrates through first-principles calculations that charge carriers can spontaneously localize in perfectly ordered one-dimensional systems due to electronic effects, challenging traditional disorder-based localization theories.

Contribution

It is the first to show that purely electronic effects can cause charge localization in ordered 1D systems using advanced computational methods.

Findings

Charge carriers spontaneously localize in ordered polymers.

Localization occurs on a nanometer scale due to exchange effects.

Lattice disorder and polaron formation follow charge localization.

Abstract

Charge carrier localization in extended atomic systems has been described previously as being driven by disorder, point defects or distortions of the ionic lattice. Here we show for the first time by means of first-principles computations that charge carriers can spontaneously localize due to a purely electronic effect in otherwise perfectly ordered structures. Optimally-tuned range-separated density functional theory and many-body perturbation calculations within the GW approximation reveal that in trans-polyacetylene and polythiophene the hole density localizes on a length scale of several nanometers. This is due to exchange-induced translational symmetry breaking of the charge density. Ionization potentials, optical absorption peaks, excitonic binding energies and the optimally-tuned range parameter itself all become independent of polymer length as it exceeds the critical localization scale. Moreover, lattice disorder and the formation of a polaron result from the charge localization in contrast to the traditional view that lattice distortions precede charge localization. Our results can explain experimental findings that polarons in conjugated polymers form instantaneously after exposure to ultrafast light pulses.