Discontinuity of the chemical potential in RDMFT for open-shell systems

TL;DR

This paper investigates the calculation of the fundamental gap in open-shell systems using reduced density-matrix functional theory, focusing on spin effects, functional choices, basis sets, and natural orbital variations.

Contribution

It derives a formula for the fundamental gap in RDMFT for open-shell systems, emphasizing the role of spin and orbital variations, which is a novel approach.

Findings

Discontinuity of the chemical potential observed in RDMFT

Impact of different functionals on gap calculations

Significance of basis set and natural orbital choices

Abstract

We employ reduced density-matrix functional theory in the calculation of the fundamental gap of open-shell systems. The formula for the calculation of the fundamental gap is derived with special attention to the spin of the neutral and the charged systems. We discuss the effects of different functionals as well as the changes due to different basis sets. Also, we investigate the importance of varying the natural orbitals for the calculation of the fundamental gap