Probing the 5f Electrons in Am-I by Hybrid Density Functional Theory

TL;DR

This paper demonstrates that hybrid density functional theory with a specific fraction of Hartree-Fock exchange accurately predicts the non-magnetic ground state and properties of Americium-I, resolving previous theoretical-experimental discrepancies.

Contribution

It shows that incorporating 40% Hartree-Fock exchange in DFT correctly reproduces Am-I's non-magnetic ground state and properties, improving theoretical predictions.

Findings

Hybrid DFT with 40% HF exchange matches experimental data.

Corrects overestimation of exchange interaction in previous models.

Predicts non-magnetic ground state consistent with experiments.

Abstract

The ground states of the actinides and their compounds continue to be matters of considerable controversies. Experimentally, Americium-I (Am-I) is a non-magnetic dhcp metal whereas theoretically an anti-ferromagnetic ground state is predicted. We show that hybrid density functional theory, which admixes a fraction of exact Hartree-Fock (HF) exchange with approximate DFT exchange, can correctly reproduce the ground state properties of Am. In particular, for a 0.40 fraction of HF exchange we obtain a non-magnetic ground state with equilibrium atomic volume, bulk modulus, 5f electron population, and the density of electronic states all in good agreement with experimental data. We argue that the exact HF exchange corrects the overestimation of the approximate DFT exchange interaction.