Water adsorption on clean Ni(111) and $p\left(2\times 2\right)\text{-Ni}\left(111\right)\text{-O}$ surfaces calculated from first principles

A systematic and comprehensive analysis of the adsorption of water monomers, small water clusters, and water thin films on clean and oxygen-predosed Ni(111) surfaces is performed. For the clean Ni surface, the formation of water hexamers (and possibly also incommensurate icelike bilayers) is favored. The total-energy results as well as the calculated vibrational frequencies for water adsorbed on the $p\left(2\times 2\right)\text{-Ni}\left(111\right)\text{-O}$ surface suggest a reinterpretation of recent experimental data [M. Nakamura and M. Ito, Phys. Rev. Lett. 94, 035501 (2005)] in terms of single water monomers adsorbed on top of Ni and the formation of (islands of) an icelike bilayer.

Figure 1

(Color online) Potential-energy surfaces for a single water monomer adsorbed on the (a) clean Ni(111) surface and $p\left(2\times 2\right)\text{-Ni}\left(111\right)\text{-O}$ surface (b) without and (c) with vdW extension. Adsorbed oxygen atoms on the surface are marked by white crosses. The positions of the ${\text{T}}_1$, ${\text{T}}_4$, and ${\text{H}}_3$ adsorption sites are indicated.

Figure 2

(Color online) Top and side views of (a) the water monomer, (b) dimer and trimer adsorption configurations, and (c) the water hexamers formed on the $p\left(2\times 2\right)\text{-Ni}\left(111\right)\text{-O}$ surface. Atomic distances are given in angstroms, with vdW-corrected results in brackets.

Figure 3

(Color online) Top views of [(a) and (b)] H-bonded hexamer structures and (c) $I_h$-like hexamer structure of water adsorbed on the $p\left(2\times 2\right)\text{-Ni}\left(111\right)\text{-O}$ surface for the following coverages $\Theta$: [(a) and (c)] 0.38 and (b) 0.5. In case of the [(a) and (b)] hexamer structure, it is energetically favorable for each surface adsorbed oxygen to accept only one H bond. However, above a coverage of 0.38 some O adatoms have to accept two H bonds, thus reducing the adsorption energy. Upper (H bonding) and lower (non-H-bonding) ${\text{H}}_2\text{O}$ molecules are indicated by U and L, respectively.

Figure 4

(Color online) Top and side views of the hexagonal icelike $\left(I_h\right)$ H-up bilayer structure adsorbed at ${\text{T}}_1/{\text{T}}_4$ sites on the $p\left(2\times 2\right)\text{-Ni}\left(111\right)\text{-O}$ surface. Atomic distances are given in angstroms, with vdW-corrected results in brackets.

Figure 5

(Color online) Top and side views of the hexagonal icelike $\left(I_h\right)$ H-down bilayer structure adsorbed at ${\text{T}}_1/{\text{T}}_4$ sites on the $p\left(2\times 2\right)\text{-Ni}\left(111\right)\text{-O}$ surface. Atomic distances are given in angstroms, with vdW-corrected results in brackets.

Figure 6

(Color online) Calculated vibrational modes assigned to experimental IR spectra from Ref. 11.