What is stable structure about Tb3N@C84? IPR or IPR-violating

The geometric and electronic structures of fullerenes encapsulating trimetallic nitride cluster Tb3N@C84 were studied using the density functional theory. Geometric optimization showed that Tb3N@C84 that violates the Isolated-Pentagon Rule (IPR) with a pentalene unit formed by fused pentagon pair is the most kinetically stable isomer with the largest energy gap. Compared to IPR-violating Tb3N@C84 isomers, IPR-Tb3N@C84 is the most thermodynamically favorable endohedral compound with the lowest energy. Tb3N@C84 has a higher density of states (DOS) than empty C84 molecule at the Fermi energy. This indicated that the embedment of Tb3N unit can increase the conductance of C84.