Density-functional theory calculations are presented for two low-energy Sm@C-76 isomers with the isolated-pentagon rule (IPR) violating cages. The relative isomeric populations at high temperatures are evaluated using the calculated molecular terms and relationships to observations are discussed.
It is shown that the observed Sm@C-2v(19138)-C-76 species can be computed as the major isomer if the encapsulate motions are treated as relatively restricted. With the restriction conjecture, the major isomer is about two times more populated than the minor Sm@C-1(17459)-C-76 endohedral.
The study points out the importance of symmetry considerations in stability evaluations for general nanocarbons.