Photoemission Spectra from Reduced Density Matrices: the Band Gap in Strongly Correlated Systems

TL;DR

This paper introduces a novel method for calculating photoemission spectra using reduced density matrices, accurately capturing the band gap in strongly correlated systems like NiO across different magnetic phases.

Contribution

The paper develops a new approach linking reduced density matrices to photoemission spectra, improving accuracy over mean-field methods in strongly correlated materials.

Findings

Accurately reproduces photoemission spectra of NiO in different magnetic phases.

Provides a qualitative description of the band gap in strongly correlated systems.

Outperforms mean-field methods in capturing insulating behavior.

Abstract

We present a method for the calculation of photoemission spectra in terms of reduced density matrices. We start from the spectral representation of the one-body Green's function G, whose imaginary part is related to photoemission spectra, and we introduce a frequency-dependent effective energy that accounts for all the poles of G. Simple approximations to this effective energy give accurate spectra in model systems in the weak as well as strong correlation regime. In real systems reduced density matrices can be obtained from reduced density-matrix functional theory. Here we use this approach to calculate the photoemission spectrum of bulk NiO: our method yields a qualitatively correct picture both in the antiferromagnetic and paramagnetic phases, contrary to mean-field methods, in which the paramagnet is a metal.