Quantum Accurate Prediction of Plutonium–Plutonium Dihydride Phase Equilibrium Using a Spin-Lattice Model

Plutonium-based materials are vital for use as nuclear fuels and as portable power sources for space vehicles. However, elucidating their sensitivity to hydriding corrosion represents an extreme challenge due to the toxicity of Pu as well as its anomalous magnetic properties. In this work, we develop a spin-lattice model of plutonium–plutonium dihydride (Pu–PuH2) phase equilibrium that retains the accuracy of density functional theory (DFT) while yielding many orders of magnitude improvement in computational efficiency. Using Monte Carlo and free energy sampling algorithms, we compute a number of Pu–PuH2 equilibrium properties that are difficult to probe experimentally, including equilibrium pressures and phase compositions at room temperature and the PuH2 heat of formation. Our method will have particular impact on these types of materials studies, where there is a strong need for computationally efficient approaches to bridge time and length scale gaps between quantum calculations and experiments.