An important class of materials problems of great interest to nuclear energy production consists of composites of metals and metal oxides, and in particular, actinide metals and actinide oxides. Individually, either type of material, actinide or oxide, can involve strong electron correlation effects. At an interface, the situation becomes even more complex. In traversing a metal-metal oxide interface, a radical compositional change is encountered. Most atomistic models address only metals, or only ceramics, but rarely both. In addition, the actinide oxides themselves enter multiple oxidation states, depending on the composition. Thus, in traversing an interface, the oxidation state need not change abruptly. As a result, these sorts of interfaces present new challenges that must be met in order to understand this important class of material systems. To address these needs, a new, ``fragment'' model Hamiltonian is constructed at the atomistic level, as opposed to the one-electron model Hamiltonians that underlie tight-binding and density functional theory methods. The model encompasses both actinides and actinide oxides, and provision is made for transitioning gradually through multiple oxidation states. The extremes of the models, the dioxides and the metals, map closely to existing models for these materials. The model for metals conforms generally to a modified embedded atom method (MEAM), meaning that the embedding function (atomistic site energy model) is analytical. The differences between the fragment Hamiltonian potential and the existing MEAM models appear in the explicit form of the embedding function and in the fact that there are two distinct terms in the embedding energy in the new model. The second term is critical to strongly-correlated-electron materials, as it is an atomistic analog to

terms appearing in Hubbard models. The model also possesses a sense of electron hopping that imparts ways to both regulate the net charge on sites in the material and to change important energy gaps that determine metallic and insulating behavior.