Electronic structure of Cr, Mn, Fe, and Co transition metal (TM) ions in GaN and AlN was calculated within generalized gradient approximation and GGA+U. The +U term was considered as a free parameter with 0 < U < 5 eV. Comparison with available data for intracenter optical transitions for Fe and Mn shows that good agreement is obtained for values of U smaller than 1 eV.
Electronic structure of Mn and Fe impurities in GaN and AlN are calculated within the density functional theory in the generalized gradient approximation without and with the +U corrections. The comparison with the available experimental data shows that the results obtained with U = 0 are in good agreement with experiment. Inclusion of +U corrections makes the agreement worse.