The difference in dispersion arises mainly from two effects. The valence-band spectrum of quartz is about 3 eV more dispersed than the valence bands of the olivines and considerably greater than the 1.4 eV difference calculated previously. For example, the Fe 3 d t 2 g and e g orbitals in M 1 and M 2 sites of the olivine are located at the top of the olivine valence band and are readily resolved in both observed spectra and theoretical calculations. The valence-band spectral contributions are readily assigned using the calculated partial density of states. GGA + U (where U is the on-site Coulomb energy) calculations on Mg-rich and Fe-rich olivines yield theoretical XPS spectra in good qualitative agreement with experiment. High-quality calculations of the band structure using pseudopotential density functional theory with generalized gradient approximation (GGA) for quartz yield a theoretical XPS valence-band spectrum in the Gelius approximation that is in excellent agreement with the experimental spectrum. The quartz and olivine valence-band spectra are very different, even though the dominant contributions to both come from molecular orbitals of Si O 4 groups. Observed total linewidths are about 1.3 eV for several of the peaks in these spectra, much narrower than previously obtained. High-resolution core-level and valence-band x-ray photoelectron spectra (XPS) of the nonconductor silicates, quartz, and two olivines ( 2 Si O 4, Mg rich and Fe rich) have been obtained with the Kratos magnetic confinement charge compensation system which minimizes differential charge broadening.

Xps peak