Optical signature for distinguishing between Mott-Hubbard, intermediate and charge-transfer insulators

Abstract

Determining the nature of band gaps in transition-metal compounds remains challenging. We present a first-principles study on electronic and optical properties of CoO using hybrid functional pseudopotentials. We show that optical absorption spectrum can provide a clear fingerprint to distinguish between Mott-Hubbard, intermediate and charge-transfer insulators. This discrimination is reflected by the qualitative difference in peak satellites due to unique interplay between $d$-$d$ and $p$-$d$ excitations, thus allowing identification from experimental data alone, unlike the existing methods that require additional theoretical interpretation. We conclude that the CoO is an intermediate, rather than a Mott-Hubbard insulator as is initially believed.

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• Advanced capabilities for materials modelling with Quantum ESPRESSO
• Many-body perturbation theory calculations using the yambo code
• Direct identification of Mott Hubbard band pattern beyond charge density wave superlattice in monolayer 1T-NbSe2

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