Spin-unrestricted zeroth order regular approximation (ZORA) and the scalar relativistic method based on Pauli Hamiltonian implemented in the Amsterdam Density Functional suite were used to calculate the electronic g tensor for isolated covalent {CuNO}(11) and electrostatic {q-NO}(1) species and for various model molecular and nonmolecular {CuNO}(11)-containing systems, epitomizing copper nitrosyl cage adducts in the ZSM-5 zeolite. The predicted g tensor values using the ZORA/VWN scheme were in satisfactory agreement with experimental EPR results. Relativistic, diamagnetic, and paramagnetic contributions to the calculated g tensor were quantified. The nature of the observed Delta g shifts was discussed in terms of the molecular orbital contributions due to the magnetic field-induced couplings and their structure sensitivity. The influence of basis set and exchange-correlation functional on the results was also briefly evaluated.