  The adsorption properties of isolated H$_{2}$O molecule on stoichiometric and
reduced (with on-surface oxygen vacancy) ceria(1111) surfaces at low coverage
are theoretically investigated by using density-functional-theory+\emph{U}
calculations and \textit{ab initio} molecular dynamics simulations. We identify
the most stable adsorption configurations on these two kinds of surfaces, which
form two hydrogen bonds between the water molecule and the oxide surface. The
electronic structures indicate that the hybridization of the molecular orbitals
of water and surface-layer O-2\emph{p} states dominates the interactions
between adsorbate and substrate. The barrier of 0.51 eV for water diffusion on
the stoichiometric surface implies the inertia of water unless up to a high
temperature of 600 K, which is confirmed by the molecular dynamics simulations.
For the reduced surface, we find that the oxygen vacancy obviously enhances the
interaction. Moreover, it is facilitated for water to dissociate into H and OH
species with a hydroxyl surface formed, instead of oxidizing the reduced
surface with the production of hydrogen gas. In addition, the molecular
dynamics simulations at low temperature 100 K confirm the dissociation process.
