We have considered in detail the effects of the low symmetry of the ${\mathrm{Fe}}^{2+}$ ion site in FeS${\mathrm{O}}_4$ on the electronic energy-level splittings and electric field gradient. Using x-ray crystallographic data and a high-speed computer, direct lattice-sum calculations have been carried out, yielding the electronic energy splittings and their corresponding eigenfunctions. Temperature depenence of quadrupole splittings calculated using these eigenfunctions is in good agreement with the experimental values taken up to 600 °K. The direction of the maximum electric field gradient at low temperatures is calculated to be nearly parallel to the crystallographic $b_0$ axis, which is consistent with neutron-diffraction and Mössbauer measurements. The ground orbital state is a single separated by $7\left|\lambda \right|$ from the first excited state, and the calculated quadrupole splitting and asymmetry factor are 3.38 mm/sec and 0.48, respectively, in agreement within experimental errors with the experimental values at low temperature.

• Received 29 June 1971

DOI:https://doi.org/10.1103/PhysRevB.4.3870