DFT/TDDFT investigation of electronic, magnetic, and optical properties of graphene containing different values of Se impurity

The electronic, magnetic, and optical properties of graphene (gr) containing selenium impurities of 2, 3, 5.5, and 12.5% were calculated by DFT. By increasing the percentage of Se impurity, the energy gap decreases from about 0.3 eV for the gr + Se (2%), to about 0.1 eV for gr + Se (3%) monolayer. Continuing this trend leads to metallic property for gr + Se (5.5%) and gr + Se (12.5%) cases. By decreasing the percentage of Se impurity as a non-thermal control parameter, the magnetization started from zero and gradually increased so that the phase transition occurred. By calculating optical properties, using TDDFT, we found that in the absorption spectrums, a visible peak appeared for the cases of Se (3%) and Se (5.5%), and in the gr + Se (12.5%) layer, there exist an infrared shoulder. Also, except for gr + Se (3%), other cases have one peak in the UVA range. Finally, in the gr + Se (2%) case, for all optical variables, the peaks are sharper and stronger, therefore this case could behave as a quantum dot.