Entanglement Measures for Single- and Multi-Reference Correlation Effects

TL;DR

This paper introduces quantum information theory-based entanglement measures to evaluate the single- and multi-reference character of molecular electronic structures, aiding in selecting appropriate quantum chemical methods.

Contribution

It proposes novel orbital entanglement measures from quantum information theory to assess electronic structure character and detect artifacts in active space choices.

Findings

Entanglement measures effectively characterize single- and multi-reference nature.

Measures identify artifacts in small active spaces.

Facilitates better method selection in quantum chemistry.

Abstract

Electron correlation effects are essential for an accurate ab initio description of molecules. A quantitative a priori knowledge of the single- or multi-reference nature of electronic structures as well as of the dominant contributions to the correlation energy can facilitate the decision regarding the optimum quantum chemical method of choice. We propose concepts from quantum information theory as orbital entanglement measures that allow us to evaluate the single- and multi-reference character of any molecular structure in a given orbital basis set. By studying these measures we can detect possible artifacts of small active spaces.