Ab initio calculation of the pleochroism of fayalite

Institut der Christian-Albrechts Universitaet, Mineralogisch-Petrographisches, Kiel, Federal Republic of Germany

Optical properties of fayalite, Fe ₂ SiO ₄ , have been obtained from ab initio calculations on the basis of the self-consistent energy band structure. The semi-relativistic, extended linear-augmented plane wave method (ELAPW) was used. Comparison of the calculated polarized optical spectra with experimental absorbance spectra shows satisfactory agreement. This observation allows a semiquantitative interpretation of the origins of the observed d-d transitions. Energy level diagrams for Fe (super 2+) ions in the M1 and M2 sites have been constructed using the Xalpha -scattered waves cluster method. These calculations quantitatively justify the use of the relationship Delta Einfinity1/R ⁵ , which is often used for the derivation of crystal-field stabilization energies at high pressures.

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