Ab Initio Polaron Wave Functions

TL;DR

This paper introduces a unified ab initio method for constructing accurate polaron wave functions across different coupling regimes, bridging large and small polaron theories with a single approach.

Contribution

A novel unitary transformation approach that interpolates between weak and strong coupling polaron theories in an ab initio framework.

Findings

Successfully applied to LiF, capturing large and small polaron behaviors.

Provides a perturbative assessment of the approach's accuracy.

Offers a new route to ab initio properties of polarons.

Abstract

In this work we demonstrate that accurate ground state wave functions may be constructed for polarons in a fully ab initio setting across the wide range of couplings associated with both the large and small polaron limits. We present a single general unitary transformation approach which encompasses an ab initio version of the Lee-Low-Pines theory at weak coupling and the coherent state Landau-Pekar framework at strong coupling while interpolating between these limits in general cases. We show that perturbation theory around these limits may be performed in a facile manner to assess the accuracy of the approach, as well as provide an independent route to the ab initio properties of polarons. We test these ideas on the case of LiF, where the electron-polaron is expected to be large and relatively weakly coupled, while the hole-polaron is expected to be a strongly coupled small polaron.