Density-functional theory ͑DFT͒ studies are performed to examine geometric and electronic properties of orthorhombic bulk V 2 O 5 as well as of its ͑010͒ oriented surface. Electronic states, total energies, as well as atom forces ͑used to obtain equilibrium geometries͒ are computed with the ab initio full-potential linear augmented plane wave method. The V 2 O 5 (010) surface is modeled by periodic single layers in a repeated slab geometry, which is justified by the weak electronic interlayer coupling found in the bulk calculations. The electronic structure of the V 2 O 5 (010) single-layer slabs, represented by their valence densities of states ͑DOS͒ and its atom contributions, is compared with results of bulk V 2 O 5 and with previous results obtained by DFT surface cluster studies. The comparison yields good qualitative agreement between the different approaches, which confirms the local nature of interatomic binding in V 2 O 5 . Further, the computed valence DOS is used to interpret recent experimental results from photoemission on V 2 O 5 (010), which suggests that differently coordinated oxygen sites at the surface can be identified in the spectrum. Thus, V 2 O 5 (010) photoemission spectra may be used to monitor the participation of oxygen ions in respective surface reactions.

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Density functional theory cluster studies and angular resolved photoemission (ARUPS) measurements were performed to examine properties of differently coordinated surface oxygens at the V 2 O 5 ( 010) surface. Calculations on embedded clusters as large as V 16 O 49 H 18 confirm the ionic character of the oxide. The computed width of the O 2sp dominated valence band region of V 2 O 5 and the work function value of V 2 O 5 (010) are in good agreement with the present photoemission data for freshly cleaved V 2 O 5 ( 010) samples. Cluster derived total and partial densities of states (DOS, PDOS) can be used to identify differently coordinated surface oxygens. The PDOS referring to terminal (vanadyl) oxygens is localized near the center of the valence band whereas the PDOS's of the different bridging oxygens yield a broad distribution covering the full energy range of the valence bands. The shape of the experimental ARUPS curves for V 2 O 5 (010) is well reproduced by the cluster DOS. Thus, the most prominent central peak in the experimental spectrum can be assigned to emission from terminal oxygen while the peripheral peaks at the top and bottom of the valence energy region are characterized as mixtures of vanadium with bridging oxygen induced contributions. This interpretation forms a basis to get insight into microscopic features at the real V 2 O 5 (010) surface such as imperfections and adsorbate binding. The present study suggests that the different O 2sp derived peaks observed in the photoemission experiment may be taken as monitors of the differently coordinated oxygens at the oxide surface and can be used to study details of catalytic surface reactions in which these oxygens participate.

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