Graphene Nanobelts, Möbius and Higher Order Möbius Strips Formed from Graphene. A Combined CASSCF/DFT Study

Twisted graphene nanoribbons with linking numbers (L_k) of 2 and 3 have been studied at hybrid DFT and CASSCF levels. CASSCF calculations demonstrated strong multireference and polyradicalic character of the ground states in all studied systems. This explains striking discrepancies between DFT and CASSCF results. We demonstrated that taking into account static correlation is important for correct description of the electronic structure of the Möbius strips. CASSCF results show the total spin and the multiconfigurational character of the ground state do not depend on the L_k. On the other hand, both DFT and CASSCF show similar trend for dependence of strain energy on the L_k. However, CASSCF results indicate higher strain energies for M3-k systems compared DFT. The increase of strain energy is more notable when going from L_k = 0 to 1 and from L_k = 2 to 3. When going from L_k = 1 to 2 the increase in strain energy is notably less.