Papers by Keyword: First-Principle

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Authors: Qing Bo Wang, Cui Zhou
Abstract: We researched the effect of single intrinsic defect of the structure and electronic properties of V-doped ZnO. After vanadium (V) atom replaced one zinc atom, lattice constants and bulk modulus increased slightly 1.2% and as high as 8.9%, respectively. The total energy showed that oxygen defect inclined to stay at a position far from V atom but zinc defect likely to localize at a position near V atom. The electronic density state of pure ZnO was semiconductor behavior. Vanadium doping introduced a spin-polarization around Fermi-level. The 3d orbital of V split into triplet-state ta (antibonding state), dual-state e (nonbonding state) and triplet-state tb (bonding state) in the wurtzite ZnO crystal field. The ta state hybridized with O2p state above Fermi-level, which made Zn15VO16 underwent a semiconductor-halfmetal transition. Vanadium substitution moved the electronic density states to lower energy. Oxygen defect had little effects on V-doped ZnO while zinc defect moved the density of states to higher energy. Our paper provided a reference for the preparation and application of V-doped ZnO.
Authors: Zhi Mei Sun, Yuan Chun Pan, Bai Sheng Sa, Jian Zhou
Abstract: On the basis of ab initio total energy calculations, we have performed an extensive study on the stacking sequence and random occupation of Ge and Sb to make the same layer in stable hexagonal Ge2Sb2Te5 (h-GST), an excellent candidate for phase change random memory applications. The results demonstrate that the atomic arrangements have great effects on lattice parameter c and electronic properties of h-GST. h-GST changes from semiconductor to metallic behavior as varying the atomic sequence.
Authors: Yue Qin Wang, Juan Gao, Shao Ping Yan
Abstract: We investigated the lattice dynamics and electron-phonon coupling (EPC) of superhard material OsB2 by first-principles linear response calculations. The calculated EPC parameters for the optical phonon modes at Г indicate that the heavy Os atoms play the most important role in deciding the superconducting behavior, and there are sizeable contributions from lighter B atoms to EPC. Our calculated EPC constant is 0.42, and the estimated superconducting transition temperature Tc is 2.1 K using the Coulomb pseudopotential μ*=0.125, in excellent agreement with the experimental ones.
Authors: Lei Feng, Fei Wang, Jia Li, Shuang Jin Wang
Abstract: The electronic structures and magnetic properties of full-Heusler alloy Ti2CoSi with Hg2CuTi-type have been investigated by first-principles calculations. The compound is predicted to be a potential half-metal ferromagnet. The calculations show that there is an energy gap in the minority spin of the band structures whereas the other spin is strongly metallic, which results in a complete spin polarization of the conduction electrons at the Fermi level. The compound has a total magnetic moment of-3.0μB per unit cell on first-principles calculations which is in excellent agreement with the SlaterPauling (SP) rule. The magnetic moments of Ti(A) atom and Ti(B) atom which are both larger than that of atom Co(C) are different. This difference comes from different atom coordination surroundings of Ti(A) and Ti(B) atoms in crystal structure.
Authors: Lei Feng, Fei Wang, Wei Zhang, Gai Yan Yang, Xi Yue Li
Abstract: The band structures and magnetic properties of Heusler alloy Cr2ZrGe with Cu2MnAl -type have been investigated by first-principles calculations. The alloy is predicted to be close to half-metal ferromagnet. The alloy has a total magnetic moment of 3.98μB per unit cell on first-principles calculations which is in agreement with the SlaterPauling (SP) rule. The magnetic moments of Cr(A) atom and Cr(C) atom which are both much larger than that of atom Zr(C) are same. This similarity comes from similar atom coordination surroundings of Cr(A) and Cr(C) atoms in crystal structure.
Authors: M. Johari Roudi, T. Mahmoodi
Abstract: Graphene is a 2D lattice of Carbon atoms which has a high potential to use it for hydrogen storage. In this paper we have studied theoretically the adsorption of hydrogen molecules on a single-layer graphene and we obtained the adsorption energy including optimized position and orientation of the hydrogen molecule with respect to the graphene surface in different points of the graphene lattice. We have done our calculations using Quantum-ESPRESSO code and applying pseudo-potential method in the framework of Density Functional Theory (DFT). We have used Local Density Approximation (LDA) for exchange correlation energy. Our result shows that adsorption energy is increased with decreasing the density of . However the maximum adsorption energy is occurred on the hollow position and for the surface homogenous arrangement.
Authors: Si Yu Yang, Lan Fang Yao, Hao Chen
Abstract: Density function theory is performed in order to investigate the effect of Ce/N co-doping on geometry structure, electronic and optical properties of anatase TiO2. Comparing the energy band and density of states of pure TiO2 and Ce/N doped anatase TiO2. We can conclude that, the valence band of pure TiO2 is main composed of O 2p states and the conduction is mainly composed of Ti 3d states. For N-doped TiO2, the topmost part of the valence band is mainly occupied by N 2p states which is higher than that of the O 2p states which can narrowed the band gap. Ce doping will introduce 4f states which is involved in the conduction band. These may lead the conduction band move down. As for Ce and N co-doped, the top of the valence band is mainly occupied by an admixture N 2p, O 2p and the bottom of the conduction band is predominantly occupied by an admixture of Ce 4f ,Ti 3d. The strong interaction between the dopants and the ions lead the band gap get narrower. We predict that Ce+N doping is one of the best choices for enhancing the photoelectrochemical activity of TiO2.
Authors: Lei Feng, Fei Wang, Jia Li, Shuang Jin Wang
Abstract: Ti-based Heusler compounds are rare reported widely up to now. In this paper, ternary full-Heusler compound Ti2NiIn is systematically studied by first-principles calculations. The calculations show the compound has a complete spin polarization around the Fermi level in the total density of state. The majority spin shows strongly metallic character, while the minority spin has an insulating behavior in its band structure. The compound has a precisely total magnetic moment of-3.0μB per formula by first-principles calculations. This result complies well with the SlaterPauling (SP) rule. All the results show that Ti2NiIn with Hg2CuTi-type structure is a new half-meltal ferromagnet by first-principles calculations.
Authors: Lei Feng, Fei Wang, Ju Gao, Jin Zhi Yin, Xiu Yan Luo
Abstract: A new Heusler alloy V2NiGa with Hg2CuTi-type structure was investigated by first-principles calculations. The band structures and magnetic properties have been studied. The alloy has a total magnetic moment of 1.05μB per unit cell on first-principles calculations which is in agreement with the SlaterPauling (SP) rule. The magnetic moments of V(1) atom and V(2) atom are 1.28μB and-0.44μB respectively, so the alloy is a ferrimagnetism.
Authors: Wen Wen Qu, Wen Jin, Jing Yu Xu, Shu Yang, Jin Hui Peng
Abstract: Zinc acetate and Zn-oxo complex of Zn4O(CH3COO)6 containing in the spent catalyst of vinyl synthesis were investigated by means of the first principles of density functional (DFT) methods. The geometries, energies, charge populations and local electron density distributions of the two compounds and their formate analogues were analyzed. Based on the pyrolysis characteristics of the spent catalyst, the thermodynamic properties of ΔG, ΔH and ΔS for possible decomposition reactions of zinc acetate and Zn4O(CH3COO)6 were calculated as functions of temperature. The results provide a theoretical evidence that Zn4O(CH3COO)6 is more stable than zinc acetate due to the regular Zn4O and ZnO4 tetrahedral coordination between Zn atoms and two kinds of O atoms. The preparation of Zn4O(CH3COO)6 via the hydrolysis of zinc acetate is thermodynamically feasible. Zn4O(CH3COO)6 is further decomposed into ZnO via a decarboxylation reaction rather than a hydrolysis reaction.
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