Computational studies on endohedral fullerenes are performed to provide information on the electronic properties of these chemical compounds. This project explores the electronic structures of endohedral fullerenes that exhibit magnetic properties, considering both endohedral metallofullerenes (including Co@C60) as well as non-metal endohedral fullerenes (including N@C60). Our interest lies in the role of functional groups attached to the endohedral fullerenes, such as pyrrolidine as well as dimers of such fullerenes in determining their magnetic properties. The computations are carried out to study the zero-field splitting of the spin states, which is a modification to the fullerene degeneracy that occurs due to the existence of unpaired electrons on the endohedral atom. All of the calculations were done using the Naval Research Laboratory Molecular Orbital Library (NRLMOL) code using density functional theory (DFT) at the all-electron generalized gradient approximation (GGA) level incorporating the Perdew-Burke-Ernzerhof (PBE) parameterization. The NRLMOL code, based on Kohn-Sham formulation of DFT, allows for the electronic structure analysis to be applied onto large structures and clusters such as endohedral fullerenes.