Endohedral fullerene Gd$_2$C$_2$@C$_{82}$ as a strongly correlated electron system

Isomerically pure endohedral fullerene with a gadolinium carbide cluster Gd$_2$C$_2$@C$_{82}$(C$_s$) has been synthesized by the electric-arc method, extracted from soot by $o$-dichlorobenzene, separated chromatographically, and characterized by mass spectroscopic and spectrophotometric methods. The energy and optical absorption spectra of the synthesized compound have been calculated for the first time within the Hubbard model. Good agreement of the experimental and calculated optical absorption curves has been observed.