Calculation of the orthorhombic E-parameter in EPR for d3 spin systems
  Third order perturbation theory is used to calculate the orthorhombic spin-Hamiltonian zero-field E-term for octahedrally surrounded d3 spin systems (S = 3/2) in strong axial fields in the presence of a weak orthorhombic component. 
Th.W.Kool
cond-mat.mtrl-sci