Modeling spin interactions in carbon peapods using a hybrid density functional theory

Abstract

The $\text{Sc}@{\text{C}}_{82}$ endohedral fullerenes inside a single-wall semiconducting or metallic nanotube form a well-defined chain of antiferromagnetically coupled spins. Using hybrid density functional theory (DFT), we find that the spin resides mainly on the fullerene cage, whether or not the fullerenes are in a nanotube. The spin interactions decay exponentially with fullerene separation and the system can be described by a simple antiferromagnetic Heisenberg spin chain. Energy parameters for a generalized Hubbard-Anderson model are deduced from the DFT calculations and yield a second-order Heisenberg exchange energy, which is in good agreement with total-energy calculations for parallel and antiparallel spin configurations. Within the accuracy of the calculations, neither semiconducting nor metallic nanotubes affect the interactions between the fullerene electron spins.