Vacancy migration of cations in uranium dioxide. A molecular dynamics simulation

A model is proposed that describes the behavior of a uranium dioxide crystal with a point defect, based on the molecular dynamics method. The model system was a face-centered cubic crystallite of 765 particles with a vacancy-type point defect. Boundary conditions were maintained through the use of a Berendsen thermostat. The purpose of the simulation was to study the migration of vacancies and cations inside the crystal at different temperatures.Migration of cations was analyzed based on the dependence of the logarithm of the diffusion coefficient of cations on the reciprocal temperature of the crystal lattice, which was constructed using the known relationship between the diffusion coefficient and the mean square displacement of atoms in the crystal. An effective diffusion activation energy of 1.10 eV was obtained, which is close to the experimental and calculated data of other authors for a single cation vacancy, which is in the range of 1.5-3.0 eV. The somewhat underestimated result can be explained by the presence of two anion vacancies next to the cation vacancy, which reduced the mobility of the vacancy cluster.