Refinement of metal d-orbital occupancies from X-ray diffraction data

Expressions are derived relating the occupancies of transition-metal d orbitals in a trigonal distortion of an octahedral field to the populations of multipole density functions refined from X-ray diffraction data. The expressions are used to obtain the iron d-orbital configuration in cubic FeS₂ by least-squares refinement of very high resolution single-crystal X-ray intensity measurements. The refined populations correspond to a large distortion of the iron electron density from spherical symmetry towards a low-spin configuration.