▎ 摘　　要

We use time dependent density functional theory to study the electronic and optical properties of rectangular graphene nanoflakes with mixed armchair and zigzag edges under uniaxial strain in order to determine the role of the size and aspect ratio. Both the HOMO-LUMO and optical bandgaps are found to exhibit strong variations under uniaxial strain, unlike two-dimensional graphene. A specific 140-atom nanoflake even is subject to a transition in the energetical order of the HOMO-1 and HOMO wavefunctions. The present work shows that through rational modifications in the aspect ratio and uniaxial strain, the electronic and optical properties of graphene nanoflakes can be favourably tuned. (C) 2017 Elsevier B.V. All rights reserved.