First-principles calculations for the adsorption of water molecules on the $\mathrm{Cu}\left(100\right)$ surface

First-principles density-functional theory and supercell models are employed to calculate the adsorption of water molecules on the $\mathrm{Cu}\left(100\right)$ surface. In agreement with the experimental observations, the calculations show that a ${\mathrm{H}}_2\mathrm{O}$ molecule prefers to bond at a onefold on-top $\left(T_1\right)$ surface site with a tilted geometry. At low temperatures, rotational diffusion of the molecular axis of the water molecules around the surface normal is predicted to occur at much higher rates than lateral diffusion of the molecules. In addition, the calculated binding energy of an adsorbed water molecule on the surfaces is significantly smaller than the water sublimation energy, indicating a tendency for the formation of water clusters on the $\mathrm{Cu}\left(100\right)$ surface.

Figure 1

Schematics of the minimum-energy structures (top view) corresponding to the configurations with a water molecule at (a) the $T_1$ site (with a tilted geometry), (b) the $T_1$ site (without a tilted geometry), (c) the $B_2$ site (without a tilted geometry), and (d) the $H_4$ site (without a tilted geometry) on the $\mathrm{Cu}\left(100\right)$ surface.

Figure 2

Schematics of the rotation of the water molecule around the surface normal in the tilted $T_1$ configuration on the $\mathrm{Cu}\left(100\right)$ surface. Note that the $\mathrm{O-Cu}$ connecting line is slightly off (by approximately $0\mathrm{.03}\mathrm{\AA }$) the rotation axis and rotates around it.

Figure 3

Total density of states (DOS) for the clean (a) and the water-adsorbed (b) $\mathrm{Cu}\left(100\right)$ surfaces and local DOS on the water molecule (c) for the water-adsorbed $\mathrm{Cu}\left(100\right)$ surface. The Fermi level is at $0\mathrm{eV}$. The calculated energy levels for the molecular orbitals of a free water molecule are also indicated in (c).