A variational approach to the optimized phonon technique for electron-phonon problems

TL;DR

This paper introduces a variational method using coherent states to efficiently truncate phonon space for numerical diagonalization of electron-phonon systems, revealing lattice distortions at intermediate couplings.

Contribution

It presents a novel variational approach that improves the efficiency of phonon space truncation in electron-phonon problem simulations.

Findings

Different lattice distortions are observed at intermediate couplings.

The approach is reliable for the extended Holstein model.

Discussion of connections with the density matrix renormalization group.

Abstract

An optimized phonon approach for the numerical diagonalization of interacting electron-phonon systems is proposed. The variational method is based on an expansion in coherent states that leads to a dramatic truncation in the phonon space. The reliability of the approach is demonstrated for the extended Holstein model showing that different types of lattice distortions are present at intermediate electron-phonon couplings as observed in strongly correlated systems. The connection with the density matrix renormalization group is discussed.