جستجوی مقالات مرتبط با کلیدواژه « density of state » در نشریات گروه « مواد و متالورژی »

In this paper, the structural and electronic properties of MoS2 and MoS2 compounds doped with cobalt in two nonmagnetic and magnetic states are investigated in the framework of the density functional theory with the Espresso quantum computing code in two exchange approximations of the generalized slope correlation and the local density of the constant charge type. The lattice constants were calculated and compared and were consistent with the results. The band structure and density of states for the MoS2 compound showed semiconducting properties. The band structure and density of states for the cobalt-doped MoS2 compound in the non-magnetic state showed metallic properties. The band structure and density of states for the cobalt-doped MoS2 composite in the magnetic state with cobalt showed weak ferromagnetism and metallic nature. The density of partial states for the composition of MoS2 shows the role of d orbital of molybdenum atom and p orbital of sulfur atom, and for MoS2 doped with cobalt, it shows the role of d orbital of cobalt atom, d orbital of molybdenum atom and p orbital of sulfur atom, which is consistent with the results of others. To compare the structural properties of the two structures, the MoS2 compound changes from the hexagonal structure to the tetragonal structure after doping with cobalt. The results are consistent with previous works.

In this research, we investigate the effects of pressure and enthalpy on the composition of molybdenum disulfide in the framework of the density functional theory and with the Espresso quantum code with flat waves and the exchange potential of the generalized slope approximation of the stationary charge. The lattice constants of the hexagonal structure of molybdenum disulfide compound were calculated and compared with other works and we have seen the agreement of the results. The electronic properties of the compound were plotted and calculated for comparison with pressure application. The band structure of molybdenum disulfide shows the semiconducting nature with a gap of about 2.27 electron volts, which is larger than the results of other researches. The density of states is plotted for the molybdenum disulfide compound and confirms the semiconducting nature of the compound. The gap obtained from the density of states is more consistent with the results of other works and its value is about 1.3 electron volts. It draws the density of partial states and shows the role of d orbital of molybdenum atom and p of sulfur atom in the overall state density. In the following, we apply different pressures, by applying constant positive pressures, the network increases, and first the bandgap decreases, then increases a little in energy, and then decreases again until the structure changes from a semiconducting nature to a metal, and by applying pressures. The lattice constant negativity is reduced and the bandgap is reduced, and in the same application of the initial pressures, it is out of the semiconducting nature and tends towards the metallic property. 

Cu2ZnSnS4 (CZTS), a quaternary material, has attracted the attention of many solar cell researchers due to its non-toxic constituents as well as their abundance on Earth. In this paper, the optical and electrical properties of the pure structure doped with the elements of the fifth group of the periodic table were investigated using the density functional theory and GGA approximation. Comparison of density of states for electrons in addition to band structures in both pure, nitrogen-doped, and phosphorus-doped bulk revealed a reduction in the direct band gap of the structure. The study of the obtained optical properties indicated the absorption coefficient increased from for the pure structure to and , respectively, for the replacement of nitrogen and phosphorus with sulfur atoms considering photons with lower energy. Substitution of arsenic, antimony and bismuth atoms instead of tin atoms, which has the lowest formation energy, causes an impurity level in the band gap due to the deganarated states. As a result, by increasing the number of electron transfer states from the valence to the conduction band, the absorption coefficient is increased to an average of for photons with lower energy in the pure structure. Consequently, reducing the gap in some cases, as well as increasing the absorption coefficient for low-energy photons after the addition of impurities, improves the performance of the CZTS plant as an adsorbent layer in solar cells.