Ground and excited states of the bipolaron in two and three dimensions

TL;DR

This paper investigates the ground and excited states of large bipolarons in two and three dimensions using a variational method, providing new energy calculations across all coupling strengths.

Contribution

It introduces a comprehensive variational approach to calculate bipolaron energies, including excited states, improving upon previous methods like Landau-Pekar.

Findings

GS and RES energies are lower than previous results

First RES state has lower energy than Franck-Condon state

Results are consistent across all coupling regimes

Abstract

The properties of large bipolarons in two and three dimensions are investigated by averaging over the relative wavefunction of the two electrons and using the Lee-Low-Pines-Huybrechts variational method. We obtain the ground-state (GS) and excited-state energies of the Fr\"{o}hlich bipolaron for the whole range of electron-phonon coupling constants. Furthermore, we calculate the energies of the first relaxed excited state (RES) and Franck-Condon (FC) excited state of the bipolaron. Compared with the FC state, the first RES has a lower energy. Our results for the GS and RES energies are lower than those obtained before by the Landau-Pekar method in the whole coupling regime.