A van der Waals density functional study of the adsorption of ethanol on the α-alumina (0001) surface

The interaction of an ethanol molecule with an α-alumina (0001) surface is investigated using density functional theory. The adsorption structure, adsorption energy, partial charges and charge densities of various non-dissociated and one dissociated structure were calculated. The results obtained using a generalised gradient approximation (GGA) functional, and three different van der Waals (vdW) functionals were compared. For every structure, the GGA functional gave the smallest adsorption energy. The vdW functionals for each structure gave adsorption energies of approximately 0.3 to 0.4 eV larger than the GGA functional, but the energetic ordering of the structures remained mostly the same with the exception of only a few almost degenerate non-dissociated structures. The dissociated structure was found to be energetically the most favorable with an adsorption energy ranging from 1.33 to 1.84 eV, depending on the functional. This is around 0.1 eV more strongly bound than the lowest energy non-dissociated structure.