Electronic structure of the extended vanadyl pyrophosphate (1 0 0) surface

Bulk and (1 0 0) surface vanadyl pyrophosphate, (VO)2P2O7, were analysed via periodic density functional theory calculations. Electronic structures were computed using the Perdew–Wang 91 functional, together with ultrasoft pseudopotentials and plane wave basis sets with cut-off energy of 400 eV. k-point sampling was restricted to the centre of the first Brillouin zone. Periodic surface models were built from one bulk unit cell, with the vacuum gap between successive layers made equal to the length of the surface slab in the direction normal to the (1 0 0) plane. Tests indicated that these conditions are sufficient to accurately model surface reactivity. Density of states (DOS) plots show that vanadium species are the primary surface electron transfer sites. Terminal PO oxygen species are the most basic surface oxygens, as indicated by their strong contribution to high-lying valence band levels. Results for periodic calculations on the (VO)2P2O7 (1 0 0) surface are hence qualitatively identical to those previously obtained from cluster calculations, with (VO)2P2O7 (1 0 0) vanadium species acting as hydrocarbon chemisorption sites, nucleophilic terminal PO oxygens performing substrate oxyfunctionalisation to non-combustion products, and protection of the mild oxidation product dependent on its orientation at the surface.