The experimental chemical shifts in the Mn and Ni complexes were used to study the efficiency of the DFT functionals and basis sets. The DFT functionals examined in this context were chosen according to their family and hierarchy , namely nonhybrid PBE, hybrid PBE0 , meta-hybrid M06 and M06-2X , range-separated hybrid CAM-B3LYP , and double-hybrid B2PLYP . Additionally, as the diamagnetic nuclear shielding and contact interaction are phenomena that are directly related to the proximity of the nucleus, the efficiency of the core augmented basis sets, namely the EPR-III , IGLO-III , aug-cc-pVTZ-J , and Jensen's pcS-3 and pcH-3 was investigated in comparison to the conventional valence basis set TZVP. The residuals of the calculated chemical shifts for both 13 C and 1 H relative to the experimental values are depicted in Fig. for the two complexes, with the mean absolute residuals (MAR) detailed in Table . On the Fe(acac) 3 complex, Pritchard et al. previously highlighted the so called "delocalization error (DE)", a nonphysical consequence of the over electron delocalizion or localization associated with an approximate DFT based calculation and its variation with different functionals . They noted that nonhybrid functionals like PBE show large DE, particularly affecting contact hyperfine interactions, while hybrid functionals with range-separated exchange, such as CAM-B3LYP, perform better. Our computed NMR shift residuals, as shown in Fig. , corroborate this observation, highlighting average and maximum residuals for each functional.