الفهرس 
Studying the Electronic and Optical Properties of Based Graphene Nano-Structures using Density Functional Theory
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Abstract
Because of its high mobility, superior thermal conductivity, exceptional mechanical properties, and high optical transparency, graphene has been the subject of significant experimental and theoretical research over the last two decades.On the other hand, the zero bandgap of pristine graphene limits its electro-optical applications. Quantum confinement in finite-size graphene structures like graphene quantum dots (GQDs) and holey GQDs could provide a way to generate a wide variety of HOMO-LUMO gaps.Using density functional theory (DFT) and time-dependent DFT, we investigate the structural stabilities and optical properties of GQDs and holey GQDs of various sizes, edge terminations, and pore passivations.The absorbance spectrum of holey GQDs is mostly influenced by pore size and pore edge passivation, with the GQD termination having a much weaker influence. The appearance of additional peaks in the absorption spectra of GQDs resulted from the production of pores. According to our results the TDDFT absorption spectra is shifted toward higher energy (blue shift) than the matching DFT absorption spectrum.The optical spectrum of GQDs is mostly influenced by their size. The spectra are red shifted for the F terminated structures compared to the H, terminated ones have small-sized pristine GQDs. Termination appears to have little effect on the electronic and optical properties of bigger GQDs.The HOMO-LUMO gap decreases as the size of the GQDs increases.Edge termination has a small effect on the spectra; shifting the absorption peaks by " ~ " 0.2 eV, which gets smaller for larger GQDs.The absorption spectra of holey GQDs appear to be mainly affected by pore passivation, while their termination causes minor shifts in their peaks. Our findings could pave the way for the development of promising materials for a number of applications, including biological applications like cell imaging, DNA detection, and sensors, as well as optoelectronic devices.