Papers by Keyword: DFT Calculation

Abstract: The reaction-limiting process for the oxidation of SiC(0001) was investigated by density functional theory calculation. I found that the oxygen molecule insertion to the interfacial SiC bonds is the limiting process and the barrier is 3.21 eV. It is also found that the CO detachment is not limiting process because the barrier becomes small when the interfacial C atom is surrounded by three O atoms.

Abstract: Metal oxide semiconducting compounds have potential application as photocatalyst materials to decompose many types of dyes and pollutants in the water. Zn₂SnO₄ and SnO₂ are semiconducting materials that have photocatalytic properties and the properties of those two semiconducting materials in the composite form have been studied. Metal oxide compounds of Zn₂SnO₄ and SnO₂ have been prepared through sonochemical methods using ZnCl₂ and SnCl₄.5H₂O as precursors. After sonication and heat treatment at 1000 °C, we could obtain Zn₂SnO₄ and SnO₂ compound in the sample as confirmed by x-ray diffraction measurement. The volume fraction of Zn₂SnO₄ and SnO₂ phases in the sample were found to be at 60 % and 40 %, respectively. The absorption spectra revealed that the band gap of the composite materials is 3.7 eV. This material could degrade all of the methylene blue with concentration of 6.0 x 10^-6 M in 120 minutes. The band structure calculation revealed that the comparable band gap values are found for Zn₂SnO₄ and SnO₂ compounds. However, the absorption edges for those compounds are slightly different, with absorption edge at 3.2 eV for SnO₂ and 3.6 eV for Zn₂SnO₄, respectively.

Abstract: In this study, a first-principles investigation of hydrogen storage in the FeTi intermetallic is carried out. The structural and electronic changes due to hydrogen insertion into the FeTi intermetallic are determined using DFT and pseudo-potential calculations through the code SIESTA (Spanish Initiative for Electronic Simulation of Thousand of Atoms). The pseudopotentials are constructed using Troullier and Martins parametrization which describes correctly the ion-electron interactions. To define the real-space grid, necessary for numerical calculations of the electron density, detailed tests were performed in order to choose the appropriate basis set, the energy cutoff and the k-grid cutoff. The exchange-correlation potential is treated with the generalized gradient approximation (GGA). Lattice data, bonding properties and the density of states provide an explanation for the role played by hydrogen in the chemical bond with the Ti and Fe constituents.

Abstract: Using density functional theory calculation, we show that oxygen (O) exhibits an interesting effect in CuInSe2. The Se atoms with dangling bonds in a Se-rich ∑3 (114) grain boundary (GB) create deep gap states due to strong interaction between Se atoms. However, when such a Se atom is substituted by an O atom, due to their smaller atomic size and stronger electronegativity, the deep gap states are shifted to lower energy regions close or even below the top of the valence band, which is beneficial to CuInSe2 solar cell.

Abstract: ABSTRACT. Solid phase FTIR and FT-Raman spectra of 1, 8-dimethylnaphthalene have been recorded in the region 3700-50 cm-1. The spectra were interpreted with aid of normal coordinate analysis based on DFT using standard B3LYP/6-31G basis sets. After scaling there is good agreement between observed and calculated frequencies. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.

Abstract: Nonresonant enhancements of third-order susceptibility χ(3)(-ω; ω, ω, -ω) have been investigated for zigzag carbon nanotube (n,0) bundles (n = 5, 7, 11, 13, 8, 10, 14, 16) based on the energy band theory combined with the classic anharmonic oscillator model. The obtained results show that the (3) values increase as circumference of tube varies in the order of 5<7<11<13 and 8<10<14<16 for (n,0) tube bundles, respectively. The origination of the large third-order susceptibility is ascribed to the circumference effect of individual tube. The nonresonant third-order susceptibility is estimated to be about 10-6 esu in the axial direction of (16,0) tube bundles, and it is possible for a good candidate to make optical phase conjugate device.

Abstract: The molecular vibrations of 1-Naphtol were investigated in polycrystalline sample, at room temperature, by FT- IR and FT-Raman spectroscopy. In parallel, ab initio and various density functional (DFT) methods were used to determine the geometrical, energetic and vibrational characteristics of 1-Naphtol . On the basis of B3LYP/6-31G* and B3LYP/6-311+G** methods and basis set combinations, a xnormal mode analysis was performed to assign the various fundamental frequencies according to the total energy distribution (TED). The vibrational spectra were interpreted, with the aid of normal coordinate analysis based on a scaled quantum mechanical force field. The Infrared and Raman spectra were also predicted from the calculated intensities. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. Simulation of Infrared and Raman spectra, utilizing the results of these calculations led to excellent overall agreement with observed spectral patterns. The investigation is performed using quantum chemical calculations conducted by means of the Gaussian 98W and Guassview set of programs. Further, density functional theory (DFT) combined with quantum chemical calculations to determine the first-order hyperpolarizability.

Abstract: The incorporation of zirconium atoms into the framework of some aluminosilicate molecular sieves can enhance the reactivities of some typical strong Brønsted acid needed reactions, and the strengthening of Brønsted acidity were regarded as one possible reason. In this study, the effects of zirconium incorporation on the Brønsted acidity of zeolite with CHA structure were characterized by means of periodic density functional theory (PDFT) calculations. Results from deprotonation energy and NH3 adsorption energy are consistent and show that no significant acidity enhancement is found in comparison to Zr-free sample. The results indicate new catalytic mechanism should exist.

Abstract: Ab initio density functional calculations were performed on a toroidal carbon C120 nanostructure with a single beryllium atom bonded to its outer surface. These calculations are based on DFT with the generalized gradient approximation PW91 (Perdew and Wang) as implemented in the Materials Studio v.4.3 code. The Dmol3 module was used to calculate, among others, total energy, charge density, HOMO-LUMO and Mulliken population analysis. On the basis of these results, the beryllium-coated toroidal carbon C120 nanostructure appears to be a good candidate for H2 storage with moderate adsorption energy.

Abstract: In this paper, we report some ab initio calculation results of three perfect stoichiometric alloy systems Ni2XGa (X = Mn, Fe, Co). The calculations have been performed on optimizing the crystal structures in both austenitic and martensitic phases, the electronic density of states (DOS), the magnetic properties and the difference of charge distributions on considering that Mn, Fe, Co are adjacent to each other within one period in the periodic table of elements, and they are all ferro-magnetic. We have shown the impact of these magnetic elements on several properties of each alloy. Study on these three Heusler alloy systems is important in view of property prediction.