International Journal of Modern Physics B

Geometrical and electronic properties of Ge${}_n$V${}^{(0,\pm 1)}$ clusters containing 1–9 Ge atoms and one V atom are calculated by using density functional theory (DFT) at the B3LYP level and the LanL2DZ basis sets. The growth pattern behavior, natural population analysis, relative stability, electronic property and magnetism of these clusters are discussed in detail. The calculation results of the geometrical show that the relative stable structures of Ge${}_n$V${}^{(0,\pm 1)}$ clusters adopt 3D structures from $n=3$ to $n=9$. The results of natural population analysis show that electrons transfer from the Ge atoms to the V atoms when $n=\mathrm{1–7}$ while the electrons transfer from the V atoms to the Ge atoms when $n=\mathrm{8–9}$. The Ge${}_n$V${}^{-}$ clusters possess higher stability and the GeV${}^{\pm 1}$, Ge₃V${}^{\pm 1}$, Ge₅V${}^{\pm 1}$, Ge₇V${}^{\pm 1}$, and Ge₉V${}^{-}$ have larger HOMO–LUMO gaps. Furthermore, the VIPs of Ge${}_n$V clusters show a reverse trend in contrast to the AIPs.

In order to fit neural model’s spiking features to electrophysiological recordings, in this paper, a fitting framework based on particle swarm optimization (PSO) algorithm is proposed to estimate the model parameters in an augmented multi-timescale adaptive threshold (AugMAT) model. PSO algorithm is an advanced evolutionary calculation method based on iteration. Selecting a reasonable criterion function will ensure the effectiveness of PSO algorithm. In this work, firing rate information is used as the main spiking feature and the estimation error of firing rate is selected as the criterion for fitting. A series of simulations are presented to verify the performance of the framework. The first step is model validation; an artificial training data is introduced to test the fitting procedure. Then we talk about the suitable PSO parameters, which exhibit adequate compromise between speediness and accuracy. Lastly, this framework is used to fit the electrophysiological recordings, after three adjustment steps, the features of experimental data are translated into realistic spiking neuron model.

In this paper, we study a model of resonant multilead point-contact tunneling by using the boundary state formulation. At a critical point, the model is described by multiflavor chiral fermions on an infinite line with a point contact interaction at the origin. By applying the folding procedure, previously developed for the model of resonant point-contact tunneling of a single lead, we map the model onto a nonchiral fermion model defined on the half line. The resonant point-contact tunneling interaction is transcribed into a nonlocal effective boundary interaction in the folded setup, where the boundary state formulation is applicable. We construct the boundary states for the models with two and three leads explicitly and evaluate the correlation functions of currents operators exactly. The electron transport between the leads is dominated by the resonant point-contact tunneling in the low frequency regime. We observe some $SU(2)$ and $SU(3)$ group theoretical structures, which may be useful to analyze more complex models.

Second harmonic generation (SHG) in a two-dimensional (2D) nonlinear photonic crystal (NPC) with finite width along $z$-direction that is embedded in air is investigated, without adopting the traditional approximations such as a plane-wave approximation (PWA) and slowly varying amplitude approximation (SVAA). The so-called quasi-phase-matching (QPM) and the corresponding SHG conversion efficiency can be modulated significantly by the field of fundamental wave (FW). It is assumed that the incident light, along $z$-direction, is normally launched upon the surface of the sample, and QPM for different directions is investigated. It is found that the QPM shows significant differences, compared with the traditional QPM along the two different directions: in the direction of finite width of the sample, the peak value of SHG conversion efficiency is deviated from the traditional case and it gets to its peak values when the transmittance resonance occurs. However, in the other direction, the deviation from the traditional QPM arises from the field modulation of the second harmonic wave (SHW) and in this direction, it is investigated that the full width at half maximum of QPM is much wider than that in the direction of finite width of the sample. These results can be used to provide a theoretical guidance for achieving QPM SHG.

Here, we deal with a model of multitype network with nonpreferential attachment growth. The connection between two nodes depends asymmetrically on their types, reflecting the implication of time order in temporal networks. Based upon graph limit theory, we analytically determined the limit of the network model characterized by a kernel, in the sense that the number of copies of any fixed subgraph converges when network size tends to infinity. The results are confirmed by extensive simulations. Our work thus provides a theoretical framework for quantitatively understanding grown temporal complex networks as a whole.

Space–time correlation analysis has become a basic and critical work in the research on road traffic congestion. It plays an important role in improving traffic management quality. The aim of this research is to examine the space–time correlation of road networks to determine likely requirements for building a suitable space–time traffic model. In this paper, it is carried out using traffic flow data collected on Beijing’s road network. In the framework, the space–time autocorrelation function (ST-ACF) is introduced as global measure, and cross-correlation function (CCF) as local measure to reveal the change mechanism of space–time correlation. Through the use of both measures, the correlation is found to be dynamic and heterogeneous in space and time. The finding of seasonal pattern present in space–time correlation provides a theoretical assumption for traffic forecasting. Besides, combined with Simpson’s rule, the CCF is also applied to finding the critical sections in the road network, and the experiments prove that it is feasible in computability, rationality and practicality.

The structural and mechanical properties of ZnS in both B3 and B1 phases have been investigated by the generalized gradient approximation (GGA) within the plane-wave pseudopotential density functional theory (DFT). The obtained lattice parameters and bulk modulus of ZnS for both B3 and B1 structures are well in line with the available theoretical and experimental results. Using the enthalpy–pressure data, we have predicted that the phase transition pressure of ZnS from B3 to B1 is 17.26 GPa, which is in good agreement with previous experimental values. The hydrostatic pressure-dependent elastic properties of the two structures, such as bulk modulus, shear modulus and Young’s modulus, are discussed. Then, the mechanical characteristics of ZnS, including ductile/brittle behavior and elastic anisotropy of the two cubic single-crystal structures, are investigated in details. Furthermore, the thermodynamic properties of ZnS under extreme condition are explored by quasi-harmonic Debye modeling. The calculated results show that the ductility and elastic anisotropy increase with pressure clearly except the ductility of B1. Besides, the temperature and pressure dependencies of the heat capacity and the Debye temperature are obtained and analyzed in the wide ranges.

For the metallic nanoparticles, smaller than the free electron path, an impact of the particle’s surface on the nonlocal effects emerging is shown. Light-induced current inside the particle begins to depend on the spatial derivatives of the field that leads to modification of Maxwell’s equations. Consequently, the results of Mie theory as well as definitions of the dielectric function and optical conductivity should be revisited. For the sphere-shaped nanoparticle, the explicit expression for the high-frequency current with account of nonlocality is obtained. The dependence of the nonlocal contribution on the light frequency and particle’s size is discussed.

In this paper, we propose the construction of asymmetric quantum codes from two families of constacyclic codes over finite field ${𝔽}_{q^2}$ of code length $n$, where for the first family, $q$ is an odd prime power with the form $4t+1$ ($t\ge 1$ is integer) or $4t-1$ ($t\ge 2$ is integer) and $n_1=\frac{q^2+1}{2}$; for the second family, $q$ is an odd prime power with the form $10t+3$ or $10t+7$ ($t\ge 0$ is integer) and $n_2=\frac{q^2+1}{5}$. As a result, families of new asymmetric quantum codes ${[[n,k,d_z/d_x]]}_{q^2}$ with $d_z$ distance larger than $q+1$ are obtained, which are not covered by the asymmetric quantum error-correcting codes (AQECCs) in Refs. 32 and 33 [J.-Z. Chen, J.-P. Li and J. Lin, Int. J. Theor. Phys. 53, 72 (2014); L. Wang and S. Zhu, Int. J. Quantum Inf. 12, 1450017 (2014)] that $d_z\le q+1$. Also, all the newly obtained asymmetric quantum codes are optimal according to the singleton bound for asymmetric quantum codes.

The melting temperatures of alkali halides (LiCl, LiF, NaBr, NaCl, NaF, NaI, KBr, KCl, KF, KI, RbBr, RbCl, RbI and CsI) have been evaluated over a wide range of pressures. The solid–liquid transition of alkali halides is of considerable significance due to their huge industrial applications. Our formalism requires a priori knowledge of the bulk modulus and the Grüneisen parameter at ambient conditions to compute $T_m$ at high pressures. The computed values are in very good agreement with the available experimental results. The formalism can satisfactorily be used to compute $T_m$ at high pressures where the experimental data are scanty. Most of the melting curves ($T_m$ versus $P$) exhibit nonlinear variation with increasing pressure having curvatures downward and exhibit a maximum in some cases like NaCl, RbBr, RbCl and RbI. The values of $T_m^{max}$ and $P_{max}$ corresponding to the maxima of the curves are given.

Using first-principles calculation method, we have investigated the zone-center phonon modes, dielectric and transport properties of the LiNbO₃-type CdPbO₃. The results show that the relatively large peaks of infrared (IR) and Raman spectra mainly come from the $E$ and $A_1$ modes, respectively. The dielectric constant calculations reveal that this compound is positive uniaxial crystal and has the large dielectric constants. By investigating the electric transport properties using gold as electrode, the interesting negative differential resistance (NDR) effect can be observed, which reveals this compound should have important application in semiconducting electronic devices.