EN
The optical band positions and spin-Hamiltonian parameters (g factors g_{i} and hyperfine structure constants A_{i}, where i=x, y, z) of the rhombic VO^{2+} complex in CsCl crystal are calculated together from two theoretical methods. One is the complete diagonalization (of energy matrix) method and another is the perturbation theory method. The calculated results from the two methods coincide and are in reasonable agreement with the experimental values. So, both methods are effective in the explanations of optical and electron paramagnetic resonance (EPR) data for d^1 ions in crystals. The calculations also suggest that in d^1 rhombic octahedra the ground state is almost a pure | d_{xy} ⟩ state. This point is different from that of conjugate d^9 (e.g., Cu^{2+}) ions in rhombic octahedra where the ground state should be an admixture of ground and first excited states.