▎ 摘　　要

We present results of our theoretical investigation on the electronic structure of graphene quantum dots (QDs). We show how the HOMO-LUMO gap can be engineered by changing their size and/or shape. We also explore the possibility of tuning the gap by functionalization with different organic groups. We find that the covalent functionalization shifts both the HOMO and LUMO energies without significantly changing the HOMO-LUMO gap. This has been explained by analysing the density of states of different functionalized graphene QDs. Our theoretical results agree well with those of the experiment on recently synthesized graphene QDs.