The electronic structures and the spin density distributions of the paramagnetic gallium 1,4-diaza(1,3)butadiene (DAB) model systems {(Bu-1-DAB)Ga(I)[Pn(SiH3)(2)]}(center dot) and the related dipnictogen species {(Bu-t-DAB)Ga[Pn(SiH3)(2)](2)}(center dot) (Pn = N, P, As) were studied using density functional theory. The calculations demonstrate that all systems share a qualitatively similar electronic structure and are primarily ligand-centered pi-radicals. The calculated electron paramagnetic resonance (EPR) hyperfine coupling constants (HFCCs) for these model systems were optimized using iterative methods and were used to create accurate spectral simulations of the parent radicals {(Bu-t-DAB)Ga(I)[Pn(SiMe3)(2)]}(center dot) (Pn = N, P, or As) and {(Bu-t-DAB)Ga[Pn(SiMe3)(2)](2)}(center dot) (Pn = P or As), the EPR spectra of which had not been simulated previously due to their complexity. Excellent agreement was observed between the calculated HFCCs and the optimum values, which can be considered the actual HFCCs for these systems. The computational results also revealed inconsistencies in the published EPR data of some related paramagnetic group 13-DAB complexes.