▎ 摘　　要

Based on first-principles study, tuning of electronic structure of graphene is reported. The emergence of band gap in this semimetal can be accomplished through different mechanisms. In this study, we have reported on the band gap modulations in graphene through chemical functionalization with oxygen, under the application of external stress, and through the creation of vacancies. Our study suggests that all these mechanisms alter either electronic properties or both structural and electronic properties of graphene. As a result, these mechanisms completely destroy the nature of massless Dirac fermions of graphene. Also, we report on the effect of static electric field on the band gap in hydrogenated graphene (graphane). The combined action of structural modifications that involves stretching and compression of C-C bonds in the hexagonal network and charge transfer mechanism are responsible for the gap opening in electronic spectrum of graphene, which is essential for the future application of graphene in electronics. The introduction of strain is a nondestructive method when compared to other methods for band gap engineering in graphene.