Photoemission Spectroscopy and Orbital Imaging from Koopmans-Compliant Functionals

TL;DR

Koopmans-compliant functionals enable accurate, first-principles prediction of molecular photoemission spectra and orbital images, aligning well with experimental data and offering a cost-effective alternative to traditional methods.

Contribution

This work demonstrates that Koopmans-compliant functionals can reliably predict spectral properties and orbital images, bridging the gap between theory and experiment in electronic structure calculations.

Findings

Accurately reproduce ultraviolet photoemission spectra.

Match experimental momentum maps of Dyson orbitals.

Offer a computationally inexpensive quasiparticle approximation.

Abstract

The determination of spectral properties from first principles can provide powerful connections between microscopic theoretical predictions and experimental data, but requires complex electronic-structure formulations that fall outside the domain of applicability of common approaches, such as density-functional theory. We show here that Koopmans-compliant functionals, constructed to enforce piecewise linearity in energy functionals with respect to fractional occupations - i.e. with respect to charged excitations - provide molecular photoemission spectra and momentum maps of Dyson orbitals that are in excellent agreement with experimental ultraviolet photoemission spectroscopy and orbital tomography data. These results highlight the role of Koopmans-compliant functionals as accurate and inexpensive quasiparticle approximations to the spectral potential.