Liquid Adsorption of Organic Compounds on Hematite α-Fe2O3 using ReaxFF

ReaxFF-based molecular dynamics simulations are used in this work to study the
effect of polarity of adsorbed molecules in the liquid phase on the structure and polarization of hematite (α-Fe₂O₃). We compared adsorption of organic molecules with different polarity on a rigid hematite surface and on a
flexible and polarizable surface. We show that the displacements of surface atoms and surface polarization in a flexible hematite model is proportional to the adsorbed molecule's polarity. The increase in electrostatic interactions resulting from charge transfer in the outermost solid atoms in a flexible hematite model results in better defined adsorbed layers, but less ordered
than those obtained assuming a rigid solid. These results suggest that care must be taken when parametrising empirical transferable force fields as the calculated charges on a solid slab in vacuum may not be representative of a real system, especially when the solid is in contact with a polar liquid.