Comment on ``Analytical expressions for zero-field splittings of 3d5 ions in low-symmetry fields and their applications''

The aims of this paper are (i) to elucidate the properties of the physical Hamiltonians and the effective spin Hamiltonians used in electron magnetic resonance and (ii) to clarify the confusion in the microscopic spin Hamiltonian approach of Zhao et al. [Phys. Rev. B 52, 10 043 (1995); 55, 8955 (1997)]. The confusion consists in an erroneous identification (or ``approximate equivalence'') of the wave functions of the two Hamiltonians and leads to invalid relations for the zero-field-splitting parameters for the S-state 3d⁵ ions at axial symmetry and the spurious numerical results.