The (010) surface of alpha-MoO3, a DFT + U study.

We apply periodic density functional theory to alpha-MoO3 and its (010) surface. The formation energy and structure of defects in the form of surface oxygen vacancies are found to depend critically on the treatment of electron localisation which is achieved in the periodic model using the DFT + U method. Calculated vibrational states for the defect free surface are found to agree well with surface science experimental data and we show that the molybdenyl stretching mode is shifted to a lower frequency in the neighbourhood of a terminal oxygen vacancy. Adsorption of molecular oxygen at the defect site can result in O2, O2(-) or O2(2-) surface species depending on the geometry of adsorption.