Effects of Magnetic Ordering on the Ground-State Energy of Plutonium Dioxide: A Study Using Adiabatic Connection Fluctuation-Dissipation Theory

Abstract Efficiency and safety improvements in nuclear fuel development demand a comprehensive understanding of the thermophysical properties of plutonium dioxide. Because of the experimental difficulty of directly measuring these properties at high temperatures, they have been supplemented by numerical simulations, such as density functional theory (DFT). While DFT struggles to accurately replicate the nonmagnetic insulating ground state of plutonium dioxide, a method called DFT+U can reproduce nonmagnetic insulating state. However, the obtained state remains more unstable than magnetic states and is not the ground state. Adiabatic connection fluctuation-dissipation theory (ACFDT) is expected to be a promising solution, addressing higher-order correlations and exact exchange energies. In this study, we evaluate the energy of the ground state using ACFDT calculations with the random phase approximation and find that the nonmagnetic state can be more stable than the magnetically ordered state. This result successfully reproduces experimental observations of the nonmagnetic ground state of plutonium dioxide and has the potential to improve the accuracy of predicting the thermophysical properties of nuclear fuel materials.