InGaAs/GaAs量子点阵列中的能级计算

根据八带k·p理论，在三维InGaAs/GaAs量子点阵列中求解k_x=k_y=k_z=0处的有效质量哈密顿H₀的本征值，得到InGaAs量子点中导带中电子基态E_C1，第一激发态E_C2和重空穴态E_{HH1关键词： InGaAs 量子点 带内跃迁 k·p理论')" href="#">八带k·p理论}     

硅纳米结点电子输运性质的计算

运用第一性原理密度泛函理论结合非平衡格林函数方法,对3个Si原子构成的直线链耦合在Au(100)面形成的三明治结构的纳米结点的电子输运进行计算.结果得到结点电导随距离的变化,当d_z=1.584 nm时,结合能最小,结构最稳定,此时Si-Si键长为0.216 nm,Si-Au键长为0.227 nm,电导为0.729 G₀(G₀=2e²/h),其电子传输通道主要由Si原子的p_x、p_y轨道电子构成;随着外电压的增大,结点的电导减小,而其I-V曲线表现出线性特征.     

Y掺杂SrTiO3晶体材料的电子结构计算

采用基于第一性原理的密度泛函理论平面波超软赝势法, 研究了Y掺杂SrTiO₃体系的空间结构和电子结构性质, 得到了优化后体系的结构参数, 掺杂形成能, 能带结构和电子态密度. 对比掺杂浓度为0125, 025, 033时,Sr_1-xY_xTiO₃和SrTi_1-xY_xO₃的掺杂形成能,发现Y替代Sr能形成更稳定的结构. 对Sr_1-xY_xTiO₃（x=0, 0125, 025, 033） 的结构进行了优化,结果表明Y替代Sr后, 随着掺杂浓度增大, 体系的晶格常数逐渐减小, 稳定性逐渐增强. 对不同掺杂浓度的Sr_1-xY_xTiO₃能带结构的计算结果表明：纯净的SrTiO₃是绝缘体, 价带顶在R点, 导带底在Γ点, 费米能级处于价带顶; 掺杂Y后, 费米能级进入到导带底中, 体系呈金属性;掺杂浓度越大,费米能级进入导带的位置越深,禁带宽度也近似变宽. 关键词： 3')" href="#">SrTiO₃ 电子结构 掺杂 VASP     

新超导体MgCNi3的虚晶掺杂研究

用全势线性缀加平面波方法,考虑局域自旋密度近似研究虚晶掺杂MgCNi₃的超导电性和磁性.计算了自旋极化能带结构、体弹性模量和它对压力的导数、原子磁矩m及其变化率.计算结果表明，对于电子掺杂的Mg_1-xAl_xCNi₃(0≤x≤0.5)，超导电性和磁涨落随掺杂量的增加逐渐减小.空穴掺杂的Mg_1-xNa_xCNi₃,在x＝0.12处出现铁磁相变，超导电性消失.在MgCNi₃少量空穴掺杂区域(0≤x<0.12)，表现为超导与磁涨落共存的不稳定状态. 关键词： 超导电性 能带结构 态密度 磁性     

第一性原理研究应变Si/(111)Si1-xGex能带结构

基于密度泛函理论框架的第一性原理平面波赝势方法对双轴应变Si/(111) Si_1-xGe_x(x=0.1—0.4)的能带结构进行了研究,结果表明：导带带边六度简并没有消除;应变部分消除了价带带边的简并度;导带带边能量极值k矢位置和极值附近可由电子有效质量描述的能带形状在应变条件下几乎不变;价带极大值附近可由空穴有效质量描述的能带形状随着x有规律地变化. 此外,给出的禁带宽度与x的拟 关键词： 应变硅 能带结构 第一性原理     

超晶格SnO2掺Cr的电子结构和光学性质的研究

基于密度泛函理论的第一性原理,采用全势线性缀加平面波方法(FPLAPW)和广义梯度近似(GGA)来处理相关能,计算了Cr掺杂SnO₂超晶格的电子态密度、能带结构、介电函数、吸收系数、反射率和折射率.研究表明由于Cr的掺入,超晶格SnO₂在费米能级附近形成了新的电子占据态,出现了不连续的杂质能带,这是由Cr-3d态和O-2p,Sn-5s态电子所形成.介电谱在0—5.5 eV之间时出现了三个新的介电峰,在高能区介电谱主峰位置发生蓝移,峰值强度减小.吸收谱、反射谱和折 关键词： 超晶格 第一性原理 态密度 电子结构     

密度泛函理论研究MgnOn(n=2—8)团簇的结构和电子性质

采用密度泛函理论中的广义梯度近似对Mg_nO_n(n=2—8)团簇的几何构型进行优化,并对能量、频率和电子性质进行了计算.结果表明,当n=2,3时,团簇的最低能量结构是平面结构;当n≥4时, 团簇的最低能量结构可以看成是由Mg₂O₂和Mg₃O₃单元组成的三维结构.O—Mg—O的钝角和较多的电荷转移对团簇的稳定性 关键词： nO_n团簇')" href="#">Mg_nO_n团簇 几何结构 电子性质     

第一性原理对GenB(n=12—19)团簇的最低能量结构及其电子性质的研究

利用第一性原理在广义梯度近似下，研究了Ge_nB(n=12—19)团簇的结构和电子性质. 结果表明：Ge_nB(n=12—19)团簇具有较大的能隙;这些团簇的最低能量结构包含有Ge₉或Ge₁₀结构单元；B原子嵌套在Ge_n团簇中和B原子替代Ge_n+1团簇的Ge原子是构成Ge_{n 关键词： n}B团簇')" href="#">Ge_nB团簇 最低能量结构 电子性质     

Ti$lt;sub$gt;2$lt;/sub$gt;B$lt;sub$gt;$lt;i$gt;n$lt;/i$gt;$lt;/sub$gt;($lt;i$gt;n$lt;/i$gt;=1–10)团簇的结构与稳定性:基于从头算的研究

采用密度泛函理论中的B3LYP方法, 结合从头算的CCSD(T)方法对Ti₂B_n(n=1–10)团簇的稳定性和电子性质进行了研究. 发现两个Ti原子的掺杂导致B_n团簇结构发生了根本性变化. 随着n的增大, Ti₂B_n团簇结构生长非常规律. 所有的最稳定结构都可看成双锥结构, 并且两个Ti原子处在双锥结构的锥顶. 根据二阶差分能量分析, 得出Ti₂B_n(n=1–10)团簇的幻数是6, 7和8. 进一步分析了团簇的Ti原子解离能、B原子解离能以及团簇的电子亲和势和电离势. 这些能量分析表明Ti₂B₆团簇既有良好的热力学稳定性, 又有良好的动力学稳定性. 应用前线轨道理论, 对Ti原子与B₆之间的成键进行了分析, 了解其稳定性的根源. 关键词： 2B_n团簇')" href="#">Ti₂B_n团簇 稳定性 从头计算 电子结构     

TiO$lt;sub$gt;2$lt;/sub$gt;纳米管电子结构和光学性质的第一性原理研究

运用基于密度泛函理论的第一性原理方法, 系统研究了小尺寸锐钛矿相(n,0)型TiO₂纳米管(D<16 Å)的几何构型、电子结构和光学性质. 结果表明: 随着管径增大, 体系单位TiO₂分子的形成能降低, 体系趋于稳定; 在管径14 Å左右, (n,0)型TiO₂纳米管会发生一次构型的转变. 能带分析显示, TiO₂纳米管的电子态比较局域化, 小管径下(D<14 Å)其导电性更好; 随着构型的转变, TiO₂纳米管由直接带隙转变为间接带隙, 并且带隙值随着管径的增大而增大, 这是由于π轨道重叠效应的影响大于量子限域效应所导致的结果. 两种效应的竞争, 使得TiO₂纳米管的介电函数虚部ε₂ (ω)谱的峰值位置随管径增大既可能红移也可能蓝移, 管径大于9 Å (即(8, 0)管)之后, TiO₂纳米管的光吸收会出现明显的增强. 关键词： 2纳米管')" href="#">TiO₂纳米管 第一性原理 电子结构 光学性质     

蜂巢光子晶格中光波的无衍射和反常折射

空间频率模式的光子带隙反映了光波在周期性结构中的线性传输特性.以这种线性传输特性为基础,研究了蜂巢光子晶格中光波的无衍射和反常折射.通过详细分析带隙结构第一通带上的衍射与折射特性,得出了光波发生反常衍射和折射的入射条件.匹配不同的入射条件,数值模拟了光波的无衍射传输和反常折射现象.结果表明:将入射光束的波矢设置在蜂巢晶格布里渊区中正常、反常衍射区的交界处,可使高斯光束沿x轴、y轴方向的衍射得到有效抑制;以多光束干涉场作为入射光场,可对蜂巢晶格进行模式匹配,激发第二布里渊区的传输模式;进一步将模式匹配后入射光场的波矢设置在反常折射区,可实现光波的反常折射.     

太赫兹场和倾斜磁场对超晶格电子动力学特性调控规律研究

微带超晶格在磁场和太赫兹场调控下表现出丰富而复杂的动力学行为, 研究微带电子在外场作用下的输运性质对于太赫兹器件设计与研制具有重要意义. 本文采用准经典的运动方程描述了超晶格微带电子在沿超晶格生长方向(z方向)的THz场和相对于z轴倾斜的磁场共同作用下的非线性动力学特性. 研究表明, 在太赫兹场和倾斜磁场共同作用下, 超晶格微带电子随时间的演化表现出周期和混沌等新奇的运动状态. 采用庞加莱分支图详细研究了微带电子在磁场和太赫兹场调控下的运动规律, 给出了电子运行于周期和混沌运动状态的参数区间. 在电场和磁场作用下, 微带电子将产生布洛赫振荡和回旋振荡, 形成复杂的协同耦合振荡. 太赫兹场与这些协同振荡模式之间的相互作用是导致电子表现出周期态、混沌态以及倍周期分叉等现象的主要原因.     

Incommensurate magnetic structure of CeSi as observed by neutron diffraction

The magnetic ordering of the orthorhombic compound CeSi (Pama space group, FeB type of structure, Z = 4) T_n = 5.6 K was investigated by means of powder neutron diffraction in the temperatures 1.5 and 10 K. Our results show that the magnetic ordering is associated with a three dimensionally amplitude-modulated phase which is incommensurate with the crystal lattice with wave vector q = (q_χ,q_y,q_z). The ordered Ce³⁺ moments are confined to the plane (a,b) at an angle of 16.7° with the b direction. It follows from the present data analysis that the dominant wave vector component is q_z, which approximately corresponds to a transversal modulation, however the incommensurateness involves also the q_x and q_y components. The amplitude of the sine wave is μ⁰_j = 1.667μ_B at 1.5 K which corresponds to quite a reduced ordered moment value compared to the Ce³⁺ free ion value gJ = 2.14μ_B.     

Measurement of electronic structure in van der Waals ferromagnet Fe5-xGeTe2

As a van der Waals ferromagnet with high Curie temperature, Fe_5-xGeTe₂ has attracted tremendous interests recently. Here, using high-resolution angle-resolved photoemission spectroscopy (ARPES), we systematically investigated the electronic structure of Fe_5-xGeTe₂ crystals and its temperature evolution. Our ARPES measurement reveals two types of band structures from two different terminations with slight k_z evolution. Interestingly, across the ferromagnetic transition, we observed the merging of two split bands above the Curie temperature, suggesting the band splitting due to the exchange interaction within the itinerant Stoner model. Our results provide important insights into the electronic and magnetic properties of Fe_5-xGeTe₂ and the understanding of magnetism in a two-dimensional ferromagnetic system.     

Preferential attachment network model with aging and initial attractiveness

In this paper, we generalize the growing network model with preferential attachment for new links to simultaneously include aging and initial attractiveness of nodes. The network evolves with the addition of a new node per unit time, and each new node has m new links that with probability Π_i are connected to nodes i already present in the network. In our model, the preferential attachment probability Π_i is proportional not only to k_i + A, the sum of the old node i's degree k_i and its initial attractiveness A, but also to the aging factor ${\tau }_{i}^{-\alpha }$, where τ_i is the age of the old node i. That is, ${{\rm{\Pi }}}_{i}\propto ({k}_{i}+A){\tau }_{i}^{-\alpha }$. Based on the continuum approximation, we present a mean-field analysis that predicts the degree dynamics of the network structure. We show that depending on the aging parameter α two different network topologies can emerge. For α < 1, the network exhibits scaling behavior with a power-law degree distribution P(k) ∝ k^−γ for large k where the scaling exponent γ increases with the aging parameter α and is linearly correlated with the ratio A/m. Moreover, the average degree k(t_i, t) at time t for any node i that is added into the network at time t_i scales as $k({t}_{i},t)\propto {t}_{i}^{-\beta }$ where 1/β is a linear function of A/m. For α > 1, such scaling behavior disappears and the degree distribution is exponential.     

Electronic structures and topological properties of TeSe2 monolayers

The successfully experimental fabrication of two-dimensional Te monolayer films [Phys. Rev. Lett. 119 106101 (2017)] has promoted the researches on the group-VI monolayer materials. In this work, the electronic structures and topological properties of a group-VI binary compound of TeSe₂ monolayers are studied based on the density functional theory and Wannier function method. Three types of structures, namely, α-TeSe₂, β-TeSe₂, and γ-TeSe₂, are proposed for the TeSe₂ monolayer among which the α-TeSe₂ is found being the most stable. All the three structures are semiconductors with indirect band gaps. Very interestingly, the γ-TeSe₂ monolayer becomes a quantum spin Hall (QSH) insulator with a global nontrivial energy gap of 0.14 eV when a 3.5% compressive strain is applied. The opening of the global band gap is understood by the competition between the decrease of the local band dispersion and the weakening of the interactions between the Se p_x, p_y orbitals and Te p_x, p_y orbitals during the process. Our work realizes topological states in the group-VI monolayers and promotes the potential applications of the materials in spintronics and quantum computations.     

Comment on the analysis of angle-dependent X-ray magnetic circular dichroism in systems with reduced dimensionality

The magnetic dipole term T appearing in the X-ray magnetic circular dichroism (XMCD) spin sum rule can be eliminated from the analysis within the spin sum rule by angle-dependent XMCD spectroscopy if the effects of spin–orbit coupling are small so that T_x+T_y+T_z≈0. It is shown by the ab initio electron theory for the extreme case of a low-dimensional system, i.e., for a free-standing monatomic Co wire that this relation is strongly violated, indicating that the determination of T by the angle-dependent XMCD is possibly not very reliable for low-dimensional magnetic systems.     

Parallel propagating modes and anomalous spatial damping in the ultra-relativistic electron plasma with arbitrary degeneracy

The dispersion relations of parallel propagating modes(Langmuir mode, right and left handed circular polarized waves) in the weak magnetic field limit |ω-k·v| ? are considered for ultra-relativistic arbitrary degenerate electron plasma. The results are presented in terms of moments of Fermi-Dirac distribution. The increase in the electron equilibrium number density from negative large(weakly degenerate) to positive large(highly degenerate) values of μ/T_e is observed(where μ is the electron chemical potential and T_e is the electron thermal energy). As a result, shifting of the cutoff points in all the real dispersion branches towards the higher values and increasing in the band gap between unmagnetized longitudinal and transverse modes in k-space are examined. Also, the suppression of the weak magnetic field effects in weakly magnetized right handed and left handed circular polarized waves and a decrease in the longitudinal and transverse screening effects are observed in the graphical patterns due to an increase in the equilibrium number density.     

Anomalous magnetotransport phenomena in θ-(BEDT-TTF)2I3

Anomalous magnetotransport phenomena have been observed in θ-(BEDT-TTF)₂I₃ crystals at temperatures below 15 K. The magnetoresistance M : (1) is a linear function of the magnetic field H, (2) is not affected by the angle between the electric current and the magnetic field, (3) but depends on the magnetic field orientation with respect to the crystal axis. Magnetoresistance is expressed as M = (aH²_a + bH²_b + cH²_c)₀^-3/2/H in terms of H = (H_a, H_b, H_c), the zero field resistivity ₀, and parameters a, b, and c which are independent of temperature and magnetic field. We have found that b a > c. Magnetoresistance up to 40 is observed for H = 7T along the b-axis at T = 1.5K.     

Existence and stability of propagating fronts for an autocatalytic reaction-diffusion system

We study a one-dimensional reaction-diffusion system which describes an isothermal autocatalytic chemical reaction involving both a quadratic (A + B → 2B) and a cubic (A + 2B → 3B) autocatalysis. The parameters of this system are in the ratio D = D_B/D_A of the diffusion constants of the reactant A and the autocatalyst B, and the relative activity k of the cubic reaction. First, for all values of D > 0 and k ≥ 0, we prove the existence of a family of propagating fronts (or travelling waves) describing the advance of the reaction. In particular, in the quadratic case k = 0, we recover the results of Billingham and Needham [Phil. Trans. R. Soc. London A 334 (1991) 1–24]. Then, if D is close to 1 and k is sufficiently small, we prove using energy functionals that these propagating fronts are stable against small perturbations in exponentially weighted Sobolev spaces. This extends part of the results that are known for the scalar equation to which our system reduces when D = 1.