Electronic, mechanical, and thermodynamic properties of americium dioxide

TL;DR

This study uses density functional theory to comprehensively analyze the electronic, mechanical, and thermodynamic properties of americium dioxide, revealing its bonding, stability, and thermal characteristics relevant for technological applications.

Contribution

It provides the first systematic DFT+U analysis of AmO₂'s properties, including electronic structure, mechanical stability, and thermal behavior, with comparisons to PuO₂.

Findings

AmO₂ is an antiferromagnetic insulator with covalent bonding similar to PuO₂.

AmO₂ is less mechanically stable against shear forces than PuO₂.

Tensile strengths of AmO₂ are lower than those of PuO₂ in key directions.

Abstract

By performing density functional theory (DFT) +$U$ calculations, we systematically study the electronic, mechanical, tensile, and thermodynamic properties of AmO$_{2}$. The experimentally observed antiferromagnetic insulating feature [J. Chem. Phys. 63, 3174 (1975)] is successfully reproduced. It is found that the chemical bonding character in AmO$_{2}$ is similar to that in PuO$_{2}$, with smaller charge transfer and stronger covalent interactions between americium and oxygen atoms. The valence band maximum and conduction band minimum are contributed by 2$p-5f$ hybridized and 5$f$ electronic states respectively. The elastic constants and various moduli are calculated, which show that AmO$_{2}$ is less stable against shear forces than PuO$_{2}$. The stress-strain relationship of AmO$_{2}$ is examined along the three low-index directions by employing the first-principles computational tensile test method. It is found that similar to PuO$_{2}$, the [100] and [111] directions are the strongest and weakest tensile directions, respectively, but the theoretical tensile strengths of AmO$_{2}$ are smaller than those of PuO$_{2}$. The phonon dispersion curves of AmO$_{2}$ are calculated and the heat capacities as well as lattice expansion curve are subsequently determined. The lattice thermal conductance of AmO$_{2}$ is further evaluated and compared with attainable experiments. Our present work integrally reveals various physical properties of AmO$_{2}$ and can be referenced for technological applications of AmO$_{2}$ based materials.