In this report density function theory calculations were used to computed ground state properties for pure and Aluminum doped nano-system (graphene/boron-nitride). Ground state calculation provide relaxation structure, molecular orbital energy, adsorption process and charge transfer. Hybrid function used in this study was (B3LYP) and basis set 6-31G*. bond length calculation for pure and doped nano-system was agreements with experimental measurements. Adsorption energy calculations show low energy raising during interaction between gas molecule and surface of nano-systems. Also, result show that type of adsorption was physical. Molecular orbital energy doesn't effect during interaction process. Charge transfer calculation show that CO gas molecule act as donor in system pure graphene, boron-nitride and Al-graphene and act as acceptor in Al-boronnitride.

In the current study, the density function theory (DFT) is used to investigate the chemical adsorption strength of NO2 gas molecule. The relaxation structure, molecular orbital energy, energy gap and adsorption energy are calculated at ground state. The time dependent DFT (TD-DFT) used to simulate excitation provides UV-Visible spectrum. There was a perpendicular geometrical orientation of the gas molecule around the surface and an adsorption distance of 2.58 Å. The adsorption distance shows the chemical reaction between the gas molecule and the surface. The result of adsorption energy indicates that the gas molecule that closed to the surface has high interaction and it decreases gradually when gas molecule goes further from the graphene nano-ribbon surface. The UV-Visible measurement indicates that the system interaction with gas molecule has red shifting in electromagnetic radiation. The final result concludes that graphene nano-ribbon has high reactivity for NO2 gas molecule. The theoretical calculations provide the ability to design optical sensor which has useful applications in an environmental monitoring.

In this study, density function theory was used to evaluate geometrical and electronic properties for pure and doped system as well as adsorption energy. Pure graphene nano-ribbon appeared in plane surface during adsorption energy to have low sensitivity to methane gas. Its energy gap changed only in distance 1A because of the chemical adsorption. Doping mechanism enhanced the proprieties of graphene nano-ribbon. In geometrical structure, copper (Cu) atom stretching the nano system and it is a sign of modification. Additionally, energy gap was decreasing by doped in transition metal atom and become opening. Adsorption energy of doped system was higher than pure nano-ribbon. It was noticed that the doped transition metal enhanced the sensitivity of the system 6 times greater than pure graphene nano-ribbon. Doping graphene nano-ribbon by copper atom revealed to be a key to design chemical and physical gas sensor for methane gas.

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In the present study, the nanostructures from curcumin dye, Phthalocyanine (Pc) dye and graphene quantum dot GQD (C30H14), as well as, the nanocomposites which include (GQD/ curcumin, 2GQD/ curcumin, GQD/ Pc and 2GQD/ Pc) are considered to investigate the performances in solar sensation. The geometrical optimization and optical properties of the studied structures are done using the density functional theory DFT and time dependent TDDFT method with B3LYP/6-31G level. Examining the evaluated structures as a sensitizer of dye-sensitized solar cells (DSSCs) by taking the TiO2 electrode and I-/I-3 electrolyte, it was found that the HOMO and LUMO energy levels, charge spatial separations, energy gap, and light harvesting efficiency for GQD/ Pc nanocomposite satisfied the requirements as a sensitizer. Therefore, it is concluded that the GQD/ Pc nanocomposite indicates an equilibrium among the multiple essential factors and it is predicted that it can be preferred as a promising sensitizer in the DSSCs compared with others structures.