▎ 摘　　要

Based on the idea that the binding energy of a graphene flake is a sum of atomic energy contributions, which depend on the local atomic environment of each atom of the flake, we propose a model for graphene flake energetics, which can very accurately predict the cohesive energy Ucoh of graphene flakes. In our study, we calculate the cohesive energy of hexagonal graphene flakes with up to approximate to 1000 atoms using the tight binding molecular dynamics method and we show that the calculated Ucoh values fit extremely accurately to the Ucoh expression derived from the proposed model. For a further validation, we show that the proposed Ucoh expression can very accurately predict the calculated Ucoh values of other graphene flakes with random shapes. Based on that model, we show that the graphene flake stability obeys the following rules: (1) Between isomers the most stable are those with the larger number of bonds (or equivalently, with the smaller number of edge atoms) and (2) between isomers with the same number of bonds (or with the same number of edge atoms), the most stable are those with the smaller number of zig-zag atoms.