The zero-field splitting of ions with $d^3$ and $d^8$ electron configurations is calculated by the perturbation theory. We consider the ionic and covalent contributions and that of anisotropic spin—spin coupling due to covalency effects. For comparison with experiment, the numerical values for ${\mathrm{V}}^{2+}$, ${\mathrm{Cr}}^{3+}$, and ${\mathrm{Ni}}^{2+}$ ions in uniaxially stressed MgO crystals are estimated.

• Received 11 January 1967

DOI:https://doi.org/10.1103/PhysRev.159.201