SUMMARY

First-principles calculations such as density functional theory (DFT) employ numerical approaches to solve the Schrodinger equation of a system. Standard functionals employed to determine the cohesive system energy, specifically the local density and generalized gradient approximations (LDA and GGA), underestimate the correlation of 5f electrons to their ions in AO2 systems (A=U,Pu,Np). The standard correction, the “Hubbard +U,” causes the multidimensional energy surface to develop a large number of local minima which do not correspond to the ground state (global minimum). Because all useful energy values derived from DFT calculations depend on small differences between large cohesive energies—often not more than one percent—comparing systems wherein one or more of the samples are not in the ground state has the potential to introduce large errors. This work presents an analysis of the fundamental issues of metastable states in both pure (e.g. UO2) and binary (e.g. U0.5Pu0.5O2) AO2 systems, and describes why current literature approaches which appear to work well for the pure compounds are not well-suited for systems containing multiple actinide species.