Onset of diradical character in small nanosized graphene patches.
A family of small graphene patches, i.e., rectangular polyaromatic hydrocarbons (PAHs), that have both zigzag and armchair edges is investigated to establish their ground state electronic structure. Broken symmetry density functional theory (DFT) and plane wave DFT were used to characterize the onset of diradical character via relative energies of open-shell and closed-shell singlet states. The perfect pairing (PP) active space approximation of coupled cluster theory was used to characterize diradical character on the basis of promotion of electrons from occupied to unoccupied molecular orbitals. The role of zigzag and armchair edges in the formation of open-shell singlet states is elucidated. In particular, it is found that elongation of the zigzag edge results in an increase of diradical character whereas elongation of the arm chair edge leads to a decrease of diradical character. Analysis of orbitals from PP calculations suggests that diradical states are formally Mobius aromatic multiconfigurational systems.
Wang
Jinhua
J
State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People's Republic of China.
Zubarev
Dmitry Yu
DY
Philpott
Michael R
MR
Vukovic
Sinisa
S
Lester
William A
WA
Cui
Tian
T
Kawazoe
Yoshiyuki
Y