جستجوی مقالات مرتبط با کلیدواژه « density functional theory dft » در نشریات گروه « فیزیک »

In this paper, electronic and structural properties such as lattice constant, energy band structure, and density of states of InP in bulk and nanowire are calculated. The calculations have been performed using the Pseudopotential method in the framework of density functional theory (DFT) with local density approximation (LDA), and generalized gradient approximation (GGA) by Quantum Espresso package. The results show a direct bandgap of 1.4 eV at the Γ point in the Brillouin zone and have not cut the Fermi level, with a good agreement with the available experimental results. Also, band structure in nanowires of about 1.49 eV was calculated, which shows an increased bulk state. The calculated results show good agreement with the available experimental results.

first principles calculation, we investigate electronic and optical properties of graphene with B, N, O and F adsorption. For the adatom studied the distortion of the graphene layer is quite significant and cause to change hybridization from sp2 to sp3 also we found that B, F and O adsorptions are n-type, p-type and direct semiconductor respectively while N adsorption has a metal behavior. N absorbed graphene show magnetic moment, while B, O and F absorbed graphene exhibit no magnetic moment. The absorption spectrum of monolayer graphene have been calculated for the cases of in plane (E⊥c), out of plane (E‖c) polarization of light and 45° to the plane of graphene layer and compared with atom adsorption on graphene and it was observed that For the case of (E⊥c) the graphene is an optical sensor for finding F atom and in the case of (E‖c) it is an optical sensor to find B atom in environment.

As a new family of 2D materials, transition metal carbides and nitrides (MXenes) have attracted growing attention in recent years due to their widespread potential applications. In this study, the electronic structures and optical properties of MXenes M2CF2 (M=Y, Lu) have been investigated using density functional theory (DFT) calculations. Based on the results, the Y2CF2 (Lu2CF2) monolayer is a semiconductor with indirect bandgap of 1.67 eV (1.42eV). Comparing the electronic bandgap of Y2CF2 and Y2CCl2 demonstrates the dependency of electronic and optical properties of these materials to the surface termination taking place during the experimental preparation of MXenes. To study the optical properties, the real and imaginary parts of the dielectric function was calculated. According to the results, there is a remarkable absorption in the ultraviolet and visible regions that they have better absorption compared to that of BP, MoS2 and Sc2CO2 monolayer compositions in the visible region. We have also considered electron energy loss function, refractive index and optical conductivity of the structures. All obtained results express that M2CF2 (M=Y, Lu) monolayers are good candidates for electronic, optoelectronic and solar energy applications.

In this study, the structural, electronic and transport properties of the (5, 0) zig-zag BN, GaAs, GaN, GaP, InN and InP nanotubes have been studied using Density Functional Theory (DFT) combined with Non-Equilibrium Green’s Function (NEGF) formalism with SIESTA software. The electronic band structure, density of states (DOS), current-voltage (I-V) characteristics and quantum conductance curves (dI/dV) of these structures were studied under low-bias conditions. The obtained results demonstrate that all of these structures exhibit semiconducting behavior but the (5, 0) zig-zag GaP nanotube has an indirect band gap which makes it suitable to use for full color displays. Instead the (5, 0) zig-zag GaAs nanotube has a smaller band gap, the highest value of the electron density of states and it showed the amazing property of Negative Differential Resistance (NDR). Therefore, it is an important candidate to use in high-speed optoelectronic devices, high-speed switching devices and high frequency oscillators.

In this study, the electron structure of the α-Al2</sub>O3</sub> rhombohedral graft has been investigated. The alpha-alumina structure belongs to the space group R3c and the rhombohedral with two units of formula (10 atoms) in the primary unit cell. Although the most widely used structure is hexagonal, it consists of 12 aluminum atoms and 18 atomic oxygen units, six units of formulas. The role of defects in the crystalline network, especially the vacancy defect, is investigated in this work. The band structure changes are evaluated in the absence of one of the O or Al atoms. The calculations showed that α-Al2</sub>O3</sub> has a direct transition at Γ, and the energy gap obtained from the density functional theory (DFT) method is 6.3 eV. Also, the depletion effect of O is higher than that of Al on the crystal electron structure: α-Al2</sub>O3</sub>:C, and is useful in increasing the response of this crystal as a detector.