U@C28: the electronic structure induced by the 32-electron principle

Abstract

First principles calculations show that the neutral U@C₂₈ has a (cage)² ground state with T_d symmetry instead of the long believed (5f)¹(cage)¹ ground state with D₂ symmetry. Its 34 valence electrons preferentially obey the 32-electron principle which fills all the s-, p-, d-, and f-type valence shells of the uranium atom. The remaining two valence electrons cannot break the electronic configuration and thus are located on the cage.