Dynamics, structure and energetics of the (111), (011) and (001) surfaces of ceria

Molecular dynamics simulations for 20–30 Å thick CeO2 slabs with 2-D periodicity are presented. The three low-index surfaces investigated are (111), (011) and (001). The simulations were performed within a constant-temperature–constant-pressure ensemble and used the shell-model to describe polarizability. All simulation runs were performed at atmospheric pressure and in the temperature range 10–1100 K. For all three surfaces at both 300 and 1100 K, we find that the surface m.s. displacements are generally larger for the oxide ions than for the cations and that the out-of-plane surface motion is usually larger than the in-plane surface motion. At room temperature, the oxygen m.s. displacements at the (111) surface are a factor 1.2 larger than in the bulk, a factor 1.6 for the (011) surface and approximately five times larger at the metastable (001) surface compared to the bulk. The effect of the presence of a surface on the ion dynamics [and on the structure for (011)] persists all the way to the slab centres, even for these rather thick slabs. Our simulations for the polar (001) surface demonstrate that the relative stabilities of different faces and surface terminations can change with temperature, and that it may not always be meaningful to consider one specific user-prepared termination as superior to the others.