We present density functional calculations of ${\mathrm{H}}_2\mathrm{O}$ interacting with the (101) and (001) surfaces of ${\mathrm{TiO}}_2$ anatase at various coverages $\theta$. On the (101) surface, nondissociative molecular adsorption at fivefold coordinated Ti sites is favored at both low and monolayer coverage. On the (001) surface, for $\theta \le 0.5$, ${\mathrm{H}}_2\mathrm{O}$ is adsorbed dissociatively, with an adsorption energy $\Delta H_{\mathrm{H},\mathrm{OH}}\sim 1.6\mathrm{eV}$. At $\theta =1\mathrm{}$, ${\mathrm{H}}_2\mathrm{O}$ can be adsorbed molecularly ( $\Delta H_{{\mathrm{H}}_2\mathrm{O}}=0.82\mathrm{}\mathrm{eV}/\mathrm{molecule}$), but a state with half of the ${\mathrm{H}}_2\mathrm{O}$ adsorbed dissociatively and the other half H bonded in a “second layer” is energetically more favorable. These results are discussed in the context of the available experimental information.

• Received 4 May 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.2954