Structures, stabilities and magnetic properties of FeCon−1 (n≤16) clusters

Under GGA, size dependence of the geometrical structures, stabilities and magnetic properties of FeCo_n−1 clusters (n≤16) have been investigated together with the Co_n clusters for comparison using DFT within the PAW method implemented in VASP. The replaced Fe atom is favorable to occupy the surface position except for FeCo₁₃. The peaks appeared at n=6, 9 and 11 for FeCo_n−1 clusters and at n=6, 9 and 12 for Co_n clusters on the size dependence of second difference of total energy imply that these clusters possess relatively higher stability. The magnetic moment is strongly correlated with the effective hybridization, which is closely related to the average bond length 〈d〉 and average coordination number 〈n_c〉. A small change in the total charge of Fe atom in FeCo_n−1 clusters will lead to a relative large reverse change in the total magnetic moment of Fe atom.     

Ab-initio calculations of electronic structure and optical properties of TiAl alloy

The electronic structures and optical properties of TiAl intermetallic alloy system are studied by the first-principle orthogonalized linear combination of atomic orbitals method. Results on the band structure, total and partial density of states, localization index, effective atomic charges, and optical conductivity are presented and discussed in detail. Total density of states spectra reveal that (near the Fermi level) the majority of the contribution is from Ti-3d states. The effective charge calculations show an average charge transfer of 0.52 electrons from Ti to Al in primitive cell calculations of TiAl alloy. On the other hand, calculations using supercell approach reveal an average charge transfer of 0.48 electrons from Ti to Al. The localization index calculations, of primitive cell as well as of supercell, show the presence of relatively localized states even above the Fermi level for this alloy. The calculated optical conductivity spectra of TiAl alloy are rich in structures, showing the highest peak at 5.73 eV for supercell calculations. Calculations of the imaginary part of the linear dielectric function show a prominent peak at 5.71 eV and a plateau in the range 1.1-3.5 eV.     

Structural and electronic properties of neutral clusters Ga12X (X=C, Si, Ge, Sn, and Pb) and their anions from first principles

The structural and electronic properties of neutral and negatively charged Ga₁₂X (X=C, Si, Ge, Sn, and Pb) clusters are calculated by the first-principles method. The results show that the most stable symmetry depends on the doped atom rather than the geometry structure. However, the geometry symmetry plays an important role in calculating the energy gap. In addition, in the anionic clusters, the added electron would reduce the energy gap by about 0.4 eV. As for the density of states (DOS), clusters with the same symmetry show a similar trend of DOS. The major impact on DOS by adding an electron is the occurrence of relative energy shift.     

Structures, phase transition, elastic properties of SnO2 from first-principles analysis

We investigate the structural, phase transition and elastic properties of SnO₂ in the rutile-type, pyrite-type, ZrO₂-type and cotunnite-type phases by the plane-wave pseudopotential density functional theory method. The lattice constants, bulk modulus and its pressure derivative are well consistent with the available experimental and other theoretical data. Also, we find that the rutile→pyrite, pyrite→ZrO₂ and ZrO₂→cotunnite phase transition occur at 12.9, 59.1 and 111.1 GPa, which are in better agreement with the experimental results than those of Gracia et al. (2007). Moreover, we obtain the pressure dependences of elastic constants for the four structures.     

NO dissociation pathways on Rh(1 0 0), (1 1 0), and (1 1 1) surfaces: A comparative density functional theory study

The chemisorption and dissociation pathways of NO on the Rh(1 0 0), (1 1 0), and (1 1 1) surfaces are studied by the plane-wave density functional theory (DFT) with CASTEP program. In addition, the electronic and geometrical effects that affect the NO dissociation reactions have been investigated in detail. The calculation results are presented as following: The effective activation energies of the best NO dissociation pathways on the Rh(1 0 0), the Rh(1 1 0), and the Rh(1 1 1) are 0.63, 0.66 and 1.77 eV, respectively. The activity of the Rh planes for NO dissociation is in the order of Rh(1 0 0) ≈ Rh(1 1 0) > Rh(1 1 1). The low dissociation barrier for Rh(1 0 0) and Rh(1 1 0) is associated with the existence of a lying-down NO structure which acts as a precursor for dissociation. By Mulliken population analysis and structure analysis, both electronic and geometrical effects are found to affect the NO dissociation reactions, but the geometrical effect exceed the electronic. The energy decomposition scheme has been used to provide further insight into the NO dissociation reactions. Based on the calculations, the interaction energy between N and O in the transition state on the Rh(1 1 1) is found much larger than that on the Rh(1 0 0) and the Rh(1 1 0). The major differences of should originate from the variation of the bonding competition effect.     

酞菁铜成膜特性的多重分形谱

运用多重分形理论,研究了酞菁铜颗粒的团聚生长成膜特性.研究表明薄膜生长是远离平衡态过程,在团聚生长中,颗粒分布有很大随机性,存在大范围的非均匀区域,这些区域具有多重分形特征.测试了酞菁铜对二氧化氮的气敏特性,结果表明通气前后,涂膜通道的频率有明显移动.     

Numerical simulation of soliton and kink density waves in traffic flow with periodic boundaries

The soliton and kink–antikink density waves are simulated with periodic boundaries, by adding perturbation in the initial condition on single-lane road based on a car-following model. They are reproduced in the form of the space–time evolution of headway, both of which propagate backwards. It is found that the solitons appear only near the neutral stability line regardless of the boundary conditions, and they exhibit upward form when the initial headway is smaller than the safety distance, otherwise they exhibit downward form. Comparison is made between the numerical and analytical results about the amplitude of kink–antikink wave, and the underlying mechanism is analyzed. Besides, it is indicated that the maximal current of traffic flow increases with decreasing safety distance. The numerical simulation shows a good agreement with the analytical results.     

Density of impurity states of shallow donors in a quantum well under intense laser field

The density of donor impurity states in a square GaAs–AlGaAs quantum well under an intense laser field is calculated taking into account the laser dressing effects on both the Coulomb potential and the confining potential. Using the effective-mass approximation within a variational scheme, the donor binding energy is obtained as a function of the laser dressing parameter, and the impurity position. Our results point out that a proper consideration of the density of impurity states may be of relevance in the interpretation of the optical phenomena related to shallow impurities in quantum wells, where the effects of an intense laser field compete with the quantum confinement.     

Volumetric, acoustic and spectroscopic studies for binary mixtures of ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) with alkoxyalkanols at T = (288.15 to 318.15) K

Densities and speeds of sound have been measured for the binary mixtures of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF₆] with ethylene glycol monoethyl ether (EGMEE), diethylene glycol monoethyl ether (Di-EGMEE), triethylene glycol monoethyl ether (Tri-EGMEE) over the whole composition range at atmospheric pressure. Experimental densities have been used to estimate excess molar volumes, V^E. Changes in isentropic compressibility, Δκ_s have been estimated by using experimental speed of sound and density values. Excess properties were fitted to the Redlich-Kister polynomial equation to obtain the binary coefficients and the standard errors. The molecular scale interactions between ionic liquid and alkoxyalkanols have been investigated through ¹H NMR spectroscopy. NMR chemical shifts for hydroxyl group of alkoxyalkanols and their deviations show hydrogen bonding interactions of varying strengths between ionic liquid and alkoxyalkanol in their binary mixtures.     

Diffusion of oxygen atom in the topmost layer of the Si(1 0 0) surface: Structures and oxidation kinetics

The incorporations and migrations of the atomic oxygen in the topmost layer Si(1 0 0)-p(2 × 2) silicon surface, are investigated theoretically using density functional theory. We show that the diffusion is dependent on the starting and the final surrounding environment and does not simply consist in hops from one silicon-silicon bond to another. The activation energies range from 0.11 eV to 2.59 eV.