Polaron versus bipolaron in conducting polymers: a density matrix renormalization group study

TL;DR

This study uses the density matrix renormalization group method to analyze the competition between polarons and bipolarons in conducting polymers, revealing how electron interactions influence their relative stability.

Contribution

It provides a systematic analysis of polaron and bipolaron stability in conjugated polymers using advanced numerical methods and includes the effects of electron-electron interactions.

Findings

Bipolaron stability depends on Hubbard U and nearest-neighbor V.

Bipolaron is more stable when U is much larger than V.

Results differ from mean field calculations in certain regimes.

Abstract

Competition between polaron and bipolaron inconjugated polymers with nondegenerate ground state is systematically studied in the extended Hubbard-Peierls model with the symmetry-breaking Brazovskii-Kirova term, using the density matrix renormalization group method combined with lattice optimization in the adiabatic approximation. We demonstrate that the relative stability of a bipolaron over two separated polarons sensitively depends on both on-site Hubbard $U$ and nearest-neighbor repulsion $V$. When $U$ is much larger than $V$, the bipolaron state is more stabilized compared with mean field calculations.