Electron energy-loss spectroscopy of the O K edge of NbO₂, MoO₂, and WO₂

Experimental high-energy transmission electron energy-loss absorption spectra from the oxygen K edges of NbO₂, MoO₂, and WO ₂ are compared with electronic structure calculations for the relevant empty states, based on the linear augmented plane wave (plus local orbital) method, in the local density approximation. These are also compared with calculations for an idealized rutile structure. The agreement of these ground-state density functional theory calculations (without core-hole effects) for these transition metal dioxides at our resolution of about 1 eV is excellent, and shows in each case an underlying structure consisting of five main peaks, despite differences in local atomic and electronic structure. We find also that shoulderlike features on an e_g peak can be related to structural distortions induced by the formation of metal-metal bonds.