Variational Lang-Firsov approach plus M\o{}ller-Plesset perturbation theory with applications to ab initio polariton chemistry

TL;DR

This paper introduces a variational Lang-Firsov approach combined with Møller-Plesset perturbation theory to accurately model electron-boson interactions in molecular systems and polariton chemistry.

Contribution

The paper develops a novel LF-MP method that improves ground state energy predictions for electron-boson coupled systems using variational optimization.

Findings

Accurate energies for Hubbard-Holstein model, diatomic molecules, and polariton-modified reactions.

Quantitative agreement with exact diagonalization and coupled-cluster results.

Analysis of multiple photon modes and spin effects.

Abstract

We apply the Lang-Firsov (LF) transformation to electron-boson coupled Hamiltonians and variationally optimize the transformation parameters and molecular orbital coefficients to determine the ground state. M\o{}ller-Plesset (MP-$n$, with $n = 2$ and $4$) perturbation theory is then performed on top of the optimized LF mean-field state to improve the description of electron-electron and electron-boson correlations. The method (LF-MP) is applied to several electron-boson coupled systems, including the Hubbard-Holstein model, diatomic molecule dissociation ($\text{H}_2$, $\text{HF}$), and the modification of proton transfer reactions (malonaldehyde and aminopropenal) via the formation of polaritons in an optical cavity. We show that with a correction for the electron-electron correlation, the method gives quantitatively accurate energies comparable to exact diagonalization or coupled-cluster theory. The effect of multiple photon modes, spin polarization, and the comparison to the coherent state MP theory are also discussed.