The heat of formation of gaseous PuO22+ from relativistic density functional calculations†
Abstract
Using a set of model reactions, we estimated the heat of formation of gaseous PuO22+ from quantum-chemical reaction enthalpies and experimental heats of formation of reference species. To this end, we carried out relativistic density functional calculations on the molecules PuO22+, PuO2, PuF6, and PuF4. We used a revised variant (PBEN) of the Perdew–Burke–Ernzerhof gradient-corrected exchange–correlation functional, and we accounted for spin–orbit interaction in a self-consistent fashion. As open-shell Pu species with two or more unpaired 5f electrons are involved, spin–orbit interaction significantly affects the energies of the model reactions. Our theoretical estimate for the heat of formation ΔfH°0(PuO22+,g), 418 ± 15 kcal mol−1, evaluated using plutonium fluorides as references, is in good agreement with a recent experimental result, 413 ± 16 kcal mol−1. The theoretical value connected to the experimental heat of formation of PuO2(g) has a notably higher uncertainty and therefore was not included in the final result.