Electronic, structural, and thermodynamic properties of mixed actinide dioxides (U, Pu, Am) O$_{2}$ from hybrid density functional theory

As a continuation of our studies of pure actinide metals using hybrid density functional theory,\footnote{R. Atta-Fynn and A. K. Ray, Europhysics Letters, \textbf{85}, 27008-p1- p6 (2009); Chemical Physics Letters, \textbf{482}, 223-227 (2009).} we present here a systematic study of the electronic and geometric structure properties of mixed actinide dioxides, U$_{0.5}$Pu$_{0.5}$O$_{2}$, U$_{0.5}$Am$_{0.5}$O$_{2}$, Pu$_{0.5}$Am$_{0.5}$ O$_{2}$ and U$_{0.8}$Pu$_{0.2}$O$_{2}$. The fraction of exact Hartree-Fock exchange used was 40{\%}. To investigate the effect of spin-orbit coupling on the ground state electronic and geometric structure properties, computations have been carried out at two theoretical levels, one at the scalar-relativistic level with no spin-orbit coupling and one at the fully relativistic level with spin-orbit coupling. Thermodynamic properties have been calculated by a coupling of first-principles calculation and lattice dynamics.