First-principles study of the adsorption of methanol at the α-Al2O3(0001) surface

We present density functional theory calculations of methanol molecular adsorption at the (0001) surface of alpha-Al2O3, for methanol coverages of 1/4 to I monolayer (ML). Adsorption energies, adsorption-induced restructuring of the surface, and induced changes to the electronic structure are calculated. We find that methanol bonds with its 0 atom to Al atoms at the alpha-Al2O3 (0001) surface with an adsorption energy of 1.23 eV at coverage 1/4 NIL, decreasing with coverage to 1.03 eV at I NIL coverage. From calculations of the relaxed adsorption geometry and the angular dependence of the total energy, we predict an orientation of the adsorbed methanol molecule that has the molecular COH plane tilted away from the surface normal. The adsorption of methanol significantly restructures alpha-Al2O3 (0001), especially for the outermost At layer. Upon adsorption a small charge transfer from the molecule to the substrate takes place.