The electronic structures and optical properties of II?III2?VI4(II = Zn, Cd; III = In; VI = Se, Te) compounds are studied by the density functional theory(DFT) using the Vienna ab initio simulation package(VASP). Geometrical optimization of the unit cell is in good agreement with the experimental data. Our calculations show that the valence band maximum(VBM) and conduction band minimum(CBM) are located at G resulting in a direct energy gap. The optical properties are analyzed, and the independent second harmonic generation(SHG) coefficients are determined. By an analysis of the band structure, we can get that SHG response of the system can be attributed to the transitions from the bands near the top of valence band that are derived from the Se/Te p states to the unoccupied bands contributed by the p states of In atoms.
The first-principles calculations were performed to investigate the stability, band structure, density of states and redox potential of Al-, Ga-, and In-doped monoclinic BiVO4(mBiVO4). The calculated formation energies show that Al-doped mBiVO4 inducing an O vacancy is energetically favorable with a smaller defect formation value. With the incorporation of Al, Ga, and In, the band gap of the doped systems will be narrowed in the order of Al-doped < Ga-doped < In-doped mBiVO4, which is beneficial for the response to the visible light. And the substitution of an Al or Ga for a V atom will significantly enhance the reducibility of mBiVO4, improving the efficiency of H2 evolution from H2 O. Our results show that the photocatalytic activity of mBiVO4 can be modulated by substitutional doping of Al, Ga, and In.
The first-principles density functional calculations are performed to study the geometries and electronic structures of HgGa2X4(X = S,Se,Te) semiconductors with defect chalcopyrite structures,and the optical properties of all crystals are investigated systematically.The results indicate that these compounds have similar band structures and the band gap decreases from S to Se to Te.For the linear optical properties,three crystals show good light transmission in the IR and part visible regions,and in particular,HgGa2S4 and HgGa2Se4 crystals possess moderate birefringence.For the nonlinear optical properties,these crystals have stronger second harmonic generation(SHG),and are theoretically predicted to have larger second-order static SHG coefficients(> 30 pm/V).The SHG of HgGa2X4(X = S,Se,Te) semiconductors can be attributed to the transitions from the bands near the top of valence band derived from X(X = S,Se,Te) p states to the unoccupied bands contributed by the p states of Ga atoms.Our results indicate that the HgGa2S4 and HgGa2Se4 compounds are good candidates for nonlinear optical crystals in the IR region.
The adsorption behavior of methyl nitrite (MN) on the closed-packed Pd(111) surface has been investigated in detail by using density functional theory (DFT). MN binds to the surface in two alternative forms, using the nitrogen atom attached to the surface. An overall net charge transfer from the substrate to the cis-MN molecule is also confirmed. In addition, the reaction mechanism for the dissociation of MN on the Pd(111) surface has been identified and compared with the methanol decomposition via O-H scission. The results demonstrate that MN is a more active reactant than methanol for the oxidative addition to the Pd catalyst. The possible reason has been analyzed from the adsorption behaviors and reaction barriers, that is, MN is chemically absorbed on the Pd(111) surface; the CH3O-NO bond scission, leading to the formation of adsorbed methoxy species, is much more favorable than that of the O-H bond scission and has a large exothermic behavior.
Density functional theory (DFT) calculations are employed to investigate the structural and electronic properties of MoS6- and MoS6 clusters. Generalized Koopmans' theorem is applied to predict the vertical detachment energies and simulate the photoelectron spectra (PES). Intriguingly, the terminal S2- , polysulfide S22- and S32- ligands simultaneously emerge in the lowest-energy structure of MoS6 . Molecular orbital analyses are performed to analyze the chemical bonding in MoS6-/0 clusters and elucidate their structural and electronic properties.
