We use ab initio, constant temperature, molecular dynamics simulations to examine some aspects of the water/solid interface. In one study we examine whether calculations of the binding energy of a molecule to a surface in vacuum have any relationship to the binding energy of the same molecule and the same surface covered by a water film. The molecules we examined were catechol and HCl and the surface was rutile TiO2(110). We calculated the binding energy of the catechol, water and HCl to the oxide surface in vacuum. Then we calculated, by ab initio molecular dynamics, the mean energy of the catechol or HCl adsorbed at the oxide/water film interface. By subtracting the energy of the water film on the oxide and the energy of gas phase catechol, we obtain the binding energy of catechol at the water/oxide interface. Next we inquired whether there may be a simple way of estimating the binding energy of the catechol at the water/oxide inteface by performing only calculations of the binding energy in vacuum. We found that the binding energy of catechol at the water/oxide interface is well approximated by the binding energy of catechol to the oxide in vacuum minus the binding energy of two water molecule to the oxide in vacuum, plus the solvation energy of two water molecules. The factor of two comes in because catechol is a large molecule and the sites to which it binds can adsorb two water molecules. Essentially The same simple formula gives a good estimate of the binding energy of HCl at the water/oxide interface except that HCl being small replaces only one water molecule. It is tempting to assume that this simple rule gives a reasonable approximation of the binding energy of other molecules to other oxides. One requirement is that the surface should be such that the water and the molecule bind to the same surface sites. We will also present results on hydrogen dissociation on RuS2(100), RuS2(111), Rh2S3(001), Rh3S4(100), and Rh17S15(100).

Simulations of water-solid interfaces

251st National Meeting (2016)

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