**Dispersion-Corrected Density Functional Theory and Classical Force Field
Calculations of Water Loading on a Pyrophyllite(001) Surface**

GZ Zhang and WA Al-Saidi and EM Myshakin and KD Jordan, JOURNAL OF PHYSICAL CHEMISTRY C, 116, 17134-17141 (2012).

DOI: 10.1021/jp305801d

Water adsorption on the (001) surface of pyrophyllite **Al(OH)(Si2O5)**
was investigated using density functional theory (DFT) with dispersion
corrections and force field calculations. The DFT calculations show that
a water molecule can bind either to one or to two basal oxygen atoms of
the surface, with adsorption energies varying from -0.10 to -0.19 eV
depending on the binding configuration and binding site. Because the
water-water interactions are stronger than the water-surface
interactions, the energetically preferred structures with two or more
molecules on the surface are clusters reminiscent of their gas-phase
counterparts. The trend in water-surface binding energies with the
number of water molecules obtained from force field calculations
qualitatively agrees with that predicted by the dispersion-corrected DFT
calculations. However, the force field calculations give a low-energy
structural motif with a water molecule coordinated to a hydroxyl group
associated with the octahedral layer of the pyrophyllite surface. This
binding motif is found to be unstable in the DFT calculations.

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