High-Temperature Thermodynamics of Uranium from Ab Initio Modeling

• Published in: Applied sciences Vol. 13; no. 4; p. 2123
• Main Authors: Söderlind, Per, Landa, Alexander, Moore, Emily E., Perron, Aurélien, Roehling, John, McKeown, Joseph T.
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.02.2023; MDPI
• Subjects: anharmonic; Anharmonicity; CALPHAD; Comparative analysis; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Density functional theory; DFT; Electronic structure; Energy; First principles; Free energy; Gibbs free energy; Heat; High temperature; Lattice vibration; Magnetic moments; Magnetism; Methods; Modelling; Molecular dynamics; Nuclear energy; Relativistic theory; specific heat; Spin-orbit interactions; Symmetry; Temperature effects; Thermal expansion; Thermodynamics; Uranium; Vibrations
• ISSN: 2076-3417; 2076-3417
• DOI: 10.3390/app13042123

We present high-temperature thermodynamic properties for uranium in its γ phase (γ-U) from first-principles, relativistic, and anharmonic theory. The results are compared to CALPHAD modeling. The ab initio electronic structure is obtained from density-functional theory (DFT) that includes spin–orbit coupling and an added self-consistent orbital-polarization (OP) mechanism for more accurate treatment of magnetism. The first-principles method is coupled to a lattice dynamics scheme that is used to model anharmonic lattice vibrations, namely, Self-Consistent Ab Initio Lattice Dynamics (SCAILD). The methodology can be summarized in the acronym DFT + OP + SCAILD. Upon thermal expansion, γ-U develops non-negligible magnetic moments that are included for the first time in thermodynamic theory. The all-electron DFT approach is shown to model γ-U better than the commonly used pseudopotential method. In addition to CALPHAD, DFT + OP + SCAILD thermodynamic properties are compared with other ab initio and semiempirical modeling and experiments. Our first-principles approach produces Gibbs free energy that is essentially identical to CALPHAD. The DFT + OP + SCAILD heat capacity is close to CALPHAD and most experimental data and is predicted to have a significant thermal dependence due to the electronic contribution.