Abstract
By using a set of model reactions, we estimated the heat of formation of gaseous UO~2~^2+^ from quantum‐chemical reaction enthalpies and experimental heats of formation of reference species. For this purpose, we performed relativistic density functional calculations for the molecules UO~2~^2+^, UO~2~, UF~6~, and UF~5~. We used two gradient‐corrected exchange‐correlation functionals (revised Perdew–Burke–Ernzerhof (PBEN) and Becke–Perdew (BP)) and we accounted for spin‐orbit interaction in a self‐consistent fashion. Indeed, spin‐orbit interaction notably affects the energies of the model reactions, especially if compounds of U^IV^ are involved. Our resulting theoretical estimates for Δ~f~${H{{^{o}\hfill \atop 0\hfill}}}$(UO~2~^2+^), 365±10 kcal mol^−1^ (PBEN) and 370±12 kcal mol^−1^ (BP), are in quantitative agreement with a recent experimental result, 364±15 kcal mol^−1^. Agreement between the results of the two different exchange‐correlation functionals PBEN and BP supports the reliability of our approach. The procedure applied offers a general means to derive unknown enthalpies of formation of actinide species based on the available well‐established data for other compounds of the element in question.