Weakly bound water structure, bond valence saturation and water dynamics at the goethite (100) surface/aqueous interface: ab initio dynamical simulations.

Water molecules adjacent to the surface were found to only weakly interact with the surface and as a result were readily able to exchange with the bulk water. To account for the large surface Fe-OH2 distances in the DFT calculations it was proposed that the surface Fe3+ atoms, which already have their bond valence fully satisfied with only five neighbors, are under-coordinated with respect to the bulk coordination. Graphical abstract All first principle calculations, at all practically achievable levels, for the goethite 100 aqueous interface support a long bond and weak interaction between the exposed surface Fe3+ and water molecules capping the surface. This result is supported by bond valence theory calculations and is indicative that each surface Fe3+ is coordinated with only 5 neighbors.