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 共查询到10条相似文献,搜索用时 15 毫秒
1.
赵文杰  王渊旭 《中国物理 B》2009,18(9):3934-3939
This paper studies the elastic and electronic structure properties of two new low-energy structures of PdN2 and PtN2 by first-principles calculations.It finds that tetragonal and monoclinic structures are more stable than a pyrite one.The always positive eigenvalues of the elastic constant matrix confirm that both the tetragonal and monoclinic structures are elastically stable.The origin of the low bulk modulus of the two structures is discussed.The results of the calculated density of states show that both of the two low-energy structures are metallic.  相似文献   

2.
Six kinds of Ni-A1 alloy nanowires are optimized by means of simulated annealing. The optimized structures show that the Ni-A1 alloy nanowires are helical shell structures that are wound by three atomic strands, which is very similar to the case with pure metallic nanowires. The densities of states (DOS), transmission function T( E), current-voltage (I - V) curves, and the conductance spectra of these alloy nanowires are also investigated. Our results indicate that the conductance spectra depend on the geometric structure properties and the ingredients of the alloy nanowires. We observe and study the nonlinear contribution to the I-V characteristics that are due to the quantum size effect and the impurity effect. The addition of Ni atoms decreases the conductance of the Ni-A1 alloy nanowire because the doping atom Ni change the electronic band structures and the charge density distribution. The interesting statistical results shed light on the physics of quantum transport at the nano-scale.  相似文献   

3.
The structures under different pressures, elastic properties, electronic structures and lattice vibrations of the X_2N_2O(X = C, Si, Ge) compounds are investigated by using the first-principle method. Based on the phonon density of state,the thermodynamic properties of the present compounds are studied under different pressures and at different temperatures. The structural parameters including the bond lengths and bond angles are in agreement with available experimental measurements and theoretical calculations. We employ the elastic theory to calculate the nine independent elastic constants(C_(ij)) and the derived elastic moduli(B, G, E, v). Results indicate that these X_2N_2O(X = C, Si, Ge) compounds are mechanically stable and show the brittle behaviors. The electronic properties of the present compounds are analyzed by using the band structure and density of states. The phonon dispersion calculations imply that the present compounds are dynamically stable. Based on the quasi-harmonic approximation, the calculations of the specific heat indicate that the temperature in a range of 0 K–1500 K and pressure in a range of 0 GPa–40 GPa have a large effect on the thermal quantities of Ge_2N_2O,compared with on those of the C_2N_2O and Si_2N_2O compounds.  相似文献   

4.
王鼎渠  周兆英  朱荣  叶雄英 《中国物理 B》2008,17(10):3875-3879
This paper reports on a method of assembling semiconducting ZnO nanowires onto a pair of Au electrodes to construct a metal--semiconductor metal (MSM) structure by dieleetrophoresis and studying on its electrical characteristics by using current-voltage (Ⅰ - Ⅴ) measurements. An electronic model with two back to back Sehottky diodes in series with a semiconductor of nanowires was established to study the electrical transport of the MSM structures. By fitting the measured Ⅰ - Ⅴ characteristics using the proposed model, the parameters of the Schottky contacts and the resistance of nanowires could be acquired. The photoelectric properties of the MSM structures were also investigated by analysing the measurements of the electrical transports under various light intensities. The deduced results demonstrate that ZnO nanowires and their Schottky contacts with Au electrodes both contribute to photosensitivity and the MSM structures with ZnO nanowires are potentially applicable for photonic devices.  相似文献   

5.
First principles calculations are preformed to systematically investigate the electronic structures, elastic and thermodynamic properties of the monoclinic and orthorhombic phases of Si C2N4 under pressure. The calculated structural parameters and elastic moduli are in good agreement with the available theoretical values at zero pressure. The elastic constants of the two phases under pressure are calculated by stress–strain method. It is found that both phases satisfy the mechanical stability criteria within 60 GPa. With the increase of pressure, the degree of the anisotropy decreases rapidly in the monoclinic phase, whereas it remains almost constant in the orthorhombic phase. Furthermore, using the hybrid density-functional theory, the monoclinic and orthorhombic phases are found to be wide band-gap semiconductors with band gaps of about 2.85 e V and 3.21 e V, respectively. The elastic moduli, ductile or brittle behaviors, compressional and shear wave velocities as well as Debye temperatures as a function of pressure in both phases are also investigated in detail.  相似文献   

6.
The stability and electronic structures of AlN nanowires with and without N-vacancy are investigated using firstprinciples calculations.We find that there is an inverse correlation between formation energy and diameter in ideal AlN nanowires.After calculating the formation energies of N-vacancy at different sites in AlN nanowires with different diameters,we find that the N-vacancy prefers to stay at the surface of the nanowires and it is easier to fabricate them under Al-rich conditions.Through studying the electronic properties of AlN nanowires with N-vacancies,we further find that there are two isolated bands in the deep part of the band gap,one of them is fully occupied and the other is half occupied.The charge density indicates that the half-fully occupied band arises from the Al at the surface,and this atom becomes an active centre.  相似文献   

7.
A planes waves pseudo-potential calculations are performed for the SrMO_4(M=Mo and W) compound in order to investigate the structural, electronic, elastic and optical properties. The calculated lattice constants are in good agreement with experiment ones. The electronic structures show that SrMO_4 has a direct band gap situated at Γpoint. The calculated elastic constants indicate that both structures are mechanically stable. The bulk modulus, shear modulus, Young's modulus and Poisson ratio are investigated from the elastic constants, in the same time the anisotropy of the elastic properties is discussed. The imaginary part of the dielectric functions is calculated and the contributions of various transitions peaks are analyzed. Furthermore, the other optical properties such as absorption coefficient I(ω),optical reflectivity R(ω), energy-loss spectrum L(ω), and the refractive index n(ω) have been investigated.  相似文献   

8.
The phase stability, thermodynamics properties and electronic structures of L12-Al3Sc and Al3Y compounds under pressure up to 40 GPa are investigated by using first-principles within a local density approximation. The results of formation energies show that Al3Sc is more stable than Al3 Y and the stability of Al3Sc will be better with the increasing pressure. The Gibbs free energy, heat capacity, Debye temperature and thermal expansion coefficient are also investigated. The decreasing density of states at the Fermi level and the strengthening Sc/Y-d orbital hybridization with Al (s, p) under high pressure lead to the observed increase of the structural stability for L12-Al3Sc and Al3 Y under pressures.  相似文献   

9.
张富春  董军堂  张威虎  张志勇 《中国物理 B》2013,22(2):27503-027503
The geometry structures,electronic structures,and magnetic properties of Zn46V2O48 nanowires are studied by density functional theory(DFT) calculations.We find that the ferromagnetic(FM) coupling is more stable for six configurations of Zn46V2O48 nanowires,and is mediated by neighboring O as evidenced from the strong hybridization of V 3d and O 2p states,exhibiting strong spin polarization.The spin polarization is found to be 100% in the Zn46V2O48 nanowires,which confirms that it is a half-metallic ferromagnet and very suitable for the injection of the spin carriers,which shows that Zn46V2O48 nanowire is one of the ideal materials to realize spin electronic devices.At the same time,the magnetic coupling mechanisms of Zn46V2O48 nanowires are analyzed with V 3d and O 2p orbitals and their magnetic moments mainly come from the contributions of the unpaired electrons of V 3d orbitals.The above results provide a theoretical basis for the preparation of 3d transition metal-doped ZnO nanowire materials.  相似文献   

10.
We have systematically studied the structures, electronic properties, and lattice dynamics of B–P compounds at high pressures. BP and B_6 P are found to be thermodynamically stable below 100 GPa, and other stoichiometries are decomposable under pressure. The predicted structures of F-43 m BP and R-3 m B_6 P are in good agreement with the experimental results by comparing the powder diffraction file(PDF) standard cards with our simulated x-ray diffractions. The bonding properties of BP and B_6 P have also been analyzed by electronic localization functions, charge density difference, and Bader charge analysis. Our results show that BP and B_6 P decompose into B and P under high pressure, which is proven to be dominated by the volumes of them. Furthermore, the infrared and Raman spectra of F-43 m and R-3 m are investigated at selected pressures and will provide useful information for future experimental studies about B–P compounds.  相似文献   

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