Anderson Impurity Mechanism for a Multi-Level Model in $\delta$-Pu

TL;DR

This study uses density functional theory with a hybrid functional to accurately model the mechanical properties of δ-plutonium, revealing the importance of orbital-selective bonding and an Anderson impurity mechanism.

Contribution

It introduces an Anderson impurity framework to explain the orbital-selective bonding observed in hybrid functional calculations of δ-Pu, improving predictive accuracy.

Findings

Hybrid functional reproduces experimental lattice parameters and elastic constants.

Orbital-selective bonding of 5f electrons is identified as key to mechanical properties.

Anderson impurity model explains the augmentation of π-bonding and volume expansion.

Abstract

Electronic correlations and spin-orbit interactions in plutonium create variations in the bonding behavior of each of its allotropes. In $\delta$-Pu, the 5f electrons lie at the tipping point between itinerant and localized behavior which makes the creation of predictive models very difficult. We perform density functional theory calculations to study the effect of correlated descriptions on the mechanical properties of $\delta$-Pu. We find that 7.5% $E_{xx}$ in the HSE functional yields the experimental lattice parameters, moreover, this functional recovers the experimental elastic constants while other approximations fail. The electronic structure of the hybrid functional yields several signatures of strong correlations including orbital-selective bonding of a single 5f electron and a pseudogap-like feature which work in tandem to improve the description of mechanical properties. We show how the emergence of orbital-selective bonding in the hybrid functional can be understood through an Anderson impurity picture which predicts the augmentation of $\pi$-bonding, the decrease of $\sigma$-bonding, and expands the volume of the cell, enabling the accurate description of the mechanical properties of $\delta$-Pu.