In this work, the electronic paramagnetic resonance (EPR) parameters g// and g^ and the hyperfine structure constants A// and A^ of vanadyl (VO2+) center in di-ammonium D-tartrate [(NH4)2C4H4O6] single crystal are theoretically studied from the high order perturbation formulas of these parameters for a 3d1 ion in tetragonally compressed octahedron. In these formulas, the energy denominators are correlated with the local structure around the impurity center and the contributions to the spin Hamiltonian parameters from the s- and p-orbitals as well as the spin-orbit coupling coefficient of the ligands are taken into account. The calculated EPR parameters are in good agreement with the experimental data
