几种纤锌矿相半金属铁磁体磁学性能的第一原理研究

通过基于密度泛函理论的第一原理计算,优化了纤锌矿结构的化合物TmZn15S16(Tm=V,Cr,Mn)的几何结构,并研究了它们的磁学性能.结果表明:TmZn15S16均为典型的半金属铁磁体,它们的超胞磁矩分别为3.0099μB,3.9977μB和5.0092μB;这些磁矩主要来源于被掺入的过渡元素;CrZn15S16的半金属特性比VZn15S16和MnZn15S16更稳定;这些半金属铁磁体的半金属带隙均比较宽,表明它们可能具有较高的居里温度;TmZn15S16中杂质过渡离子的电子结构分别为V:eg2↑t12g↑,Cr:eg2↑t22g↑和Mn:eg2↑t32g↑.     

Influences of supercell termination and lateral row number on the determination of slow light properties of photonic crystal waveguides

We systematically analyze the effects of the use of an inaccurate supercell termination and an insufficient supercell size of plane-wave expansion method on the dispersion and the slow light properties of the photonic crystal waveguides. The inattentive use of supercells of photonic crystal waveguides appeared in the literature is found to be yielding errors in the dispersion and slow light characteristics of the fundamental guided mode of photonic crystal waveguides. In addition, extra modes appear in the photonic band gap of the photonic crystal waveguide due to inaccurate supercell termination. By examining the field distribution of the modes, the extra modes can be determined and removed from the band diagram. The dispersion, group index and bandwidth characteristics are observed to be less affecting from inaccurate supercell termination as the number of rows adjacent to the waveguide increases. Moreover, the dispersion and the group index-frequency curves of the fundamental guided mode of correctly terminated supercells are found to be converging as the lateral row number along the line-defect is increased.     

光子晶体光纤中自相位调制效应对超高斯脉冲传输的影响

为了研究光子晶体光纤的微结构对其非线性光传输特性的影响,利用超格子法和光子晶体光纤中的光传输方程,计算了光子晶体光纤中的高斯光脉冲和超高斯脉冲的自相位调制谱.计算结果表明：高斯光脉冲和超高斯光脉冲的高频端比低频端均有较大的频谱展宽,而高斯光脉冲的频谱比超高斯光脉冲的频谱具有更大的中心峰值;超高斯光脉冲较高斯光脉冲有较广的频谱范围,它们的自相位调制展宽范围均随着传输距离的增加而增大.这些现象均可以利用自陡峭效应的理论加以解释.与传统光纤相比,高斯光脉冲在传统光纤中所受自相位调制效应的影响较小.     

Au钝化Si(100)表面的电子特性

用TB-LMTO方法研究单层的Au原子在理想的Si(100)表面的化学吸附.计算了Au原子在不同位置的吸附能,吸附体系与清洁Si(100)表面的层投影态密度, 以及电子转移情况.结果表明, Au原子在吸附面上方的A位(顶位)吸附最稳定, Au钝化Si(100)表面可以取得明显的钝化效果, 这一结论与实验事实相符合.     

Adsorption of Ag on Si(1 0 0) surface

The chemisorption of one monolayer Ag atoms on an ideal Si(1 0 0) surface is studied by using the self-consistent tight-binding linear muffin-tin orbital method. The adsorption energies (E_ad) of different sites are calculated. It is found that the adsorbed Ag atoms are more favorable on C site (fourfold site) than on any other sites on Si(1 0 0) surface, the polar covalent bond is formed between Ag atom and surface Si atom, a Ag and Si mixed layer does not exist and does form an abrupt interface at the Ag–Si(1 0 0) interface. This is in agreement with the experiment results. The layer-projected density of states is calculated and compared with that of the clean surface. The charge transfer is also investigated. Comparing with the Au/Si(1 0 0) system, the interaction is weaker between Ag and Si than between Au and Si.     

ZnS掺Mn2+电子结构和光学性质的第一性原理计算

在广义梯度近似下,利用平面波赝势对ZnS(闪锌矿, F-43m)和Mn2+掺杂的ZnS超晶胞的电子态密度、原子间电子云重叠布局数和光学性质等进行了自恰计算。自旋极化的计算结果显示,掺入Mn2+离子后态密度整体向低能方向移动,在禁带中出现了由Mn 3d、Zn3d与S 3p组成的新态。电子云重叠布局分析了掺杂前后价键性质的变化,解释了磁性离子Mn2+导致Zn和S出现不对称的自旋向上和自旋向下态的机理。复介电系数谱图向高能方向迁移,并且在0到2.7eV范围内出现一个新的尖峰,利用晶体场理论和态密度,对改介电峰进行了指认,为研究此类材料光学性质提供了一定理论依据。     

平板二维声子晶体声波能带结构研究

利用超元胞法,研究由钢板上生长有限长度的钢柱体形成的散射体嵌入环氧树脂基体中所构成的平板二维声子晶体的声波能带结构,分析散射体的几何参数如柱体的高、半径和板的厚度对声波带隙的影响。研究结果表明:(1)这种新型的声子晶体具有很宽的带隙,且带隙出现在低频范围内;(2)散射体的几何参数对带隙的宽度有很大的影响,它们是控制带隙宽度的主要因素。     

空位缺陷对单层硅烯薄膜力学性能的影响

采用基于分子动力学理论的Forcite模拟软件包对含不同浓度的单、双空位缺陷硅烯薄膜的超晶胞体系进行优化,并对其力学性能进行了计算和分析.结果表明:随着空位缺陷浓度的增加,硅烯薄膜的拉梅常数、泊松比、体弹模量和剪切模量呈线性递减趋势,而由于空位缺陷附近键长的缩减导致硅烯薄膜"硬化"与空位缺陷浓度的增加导致硅烯晶格中硅原子密度降低,两种体制的竞争使得硅烯杨氏模量表现出先升高在降低的趋势.     

Photoemission experiments and density functional calculations for the W(1 1 2) stepped surface with submonolayer Au coverages

Photoemission experiments and theoretical calculations for the system Au-stepped W(1 1 2), have been done at submonolayer coverage region ranging from 0.1 to 0.9 monolayers, for different sample orientations relative to the photon polarization, i.e. parallel and perpendicular to the steps direction. Valence-band photoemission spectra of the Au/W(1 1 2) system demonstrate sharp angular dependent features at 4.5 and 0.3 eV binding energies when the photon polarization is parallel to the steps direction. Density functional theory calculations were performed for the Au/W(1 1 2) system with monolayer and half monolayer Au coverages in order to assign the origin of these features.