The results of quantum-chemical calculations of the molecular structure parameters (bond lengths, bond and torsion angles) of the trans-chelate of Ni(II) with hydrazinomethanethioamide obtained by different versions of the density functional theory (DFT) method and GAUSSIAN09 program are summarized. The calculated data were compared with the corresponding experimental data. Although the structural data obtained using different methods of DFT are in good agreement with experiment they give different results in the evaluation of the spin multiplicity of the ground state and the relative energies between ground and excited states. The best agreement with experiment was observed in the calculation by OPBE/TZVP method.