Structural, electronic, optical, and magneto-optical properties of Bi12MO20 (M5Ti, Ge, Si) sillenite crystals from first principles calculations

The structural, electronic, optical, and magneto-optical properties of the three Bi12MO20 sillenites (BMO; M = Ti, Ge, and Si) have been investigated on the basis of the first-principles calculations performed by the full potential augmented plane wave method. The BMO’s linear optical responses are found to be very similar, but their optical rotatory powers and Faraday ellipticities exhibit notable differences in both visible and ultraviolet parts of the spectra. These differences originate from the subtle differences within the BMO’s electronic structures, such as different band-gaps and different offsets of the valence band tops. The latter are found to be caused not by the influence of the M ion electronic states, but by particular behavior of the M–O and the Bi–O chemical bonds