Uranyl molybdates are important materials for the pyrochemical reprocessing of spent nuclear fuel. Progress in first-principles atomistic modeling and simulation of these materials is desirable but complicated by the presence of $f$ electrons, the effects of strong electron correlations, and the scarcity of experimental data for the validation of models. In this work, we present a first-principles model of solid-phase uranyl molybdates based on the DFT + U level of theory. Initially, pure ${\mathrm{UO}}_2{\mathrm{MoO}}_4$ is synthesized, characterized, and diffuse reflectance spectroscopy is utilized in order to facilitate the validation of such a first-principles model, which is then applied to various sodium-bearing uranates, molybdates, and uranyl molybdates. Crystal structures and formation enthalpies are considered as well as the electronic properties of ${\mathrm{UO}}_2{\mathrm{MoO}}_4$ and the polymorphism of ${\mathrm{Na}}_2{\mathrm{UMo}}_2{\mathrm{O}}_{10}$. Apart from ${\mathrm{UO}}_2{\mathrm{MoO}}_4$, we present independent experimental results for ${\mathrm{Na}}_2{\mathrm{UMo}}_2{\mathrm{O}}_{10}$ by solving controversies in the numerous structural data attributed to this compound.

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• Electronic structure
• First-principles calculations
• Thermodynamics
• Actinides
• Crystal structures
• Strongly correlated systems
• Differential thermal analysis
• Scanning electron microscopy
• X-ray diffraction