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Tight—binding calculation of the electronic states of bulk—terminated GaAs(311)A and B surfaces 下载免费PDF全文
We have carried out theoretical investigations on the electronic structure of GaAs(311)A and GaAs(311)B surfaces. The bulk electronic structure of GaAs has been described by the second-neighbour tight-binding formalism and the surface electronic structure was evaluated via an analytic Green function method. First, we present the surface band structure together with the projected bulk band of both Ga-terminated and As-terminated for GaAs(311)A and GaAs(311)B surfaces, respectively. In each case, the number of surface states is determined, and the localized surface features and orbital properties of these surface states along Γ-Y-S-X-Γ high symmetry lines of the surface Brillouin zone are discussed. For the Ga-terminated GaAs(311)A (1×1) surface, we have tested two possible structure models, i.e. "the bridge site" and "the hollow site" models. In comparison with the angle-resolved photoelectron spectroscopy studied recently, the results have shown that the surface electronic states of the hollow site model are in good agreement with the experiments, whereas those of the bridge site model are not. So we have concluded that the hollow site model is favourable for the Ga-terminated GaAs(311) (1×1) surface and the bridge site model should be excluded. 相似文献
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1 INTRODUCTION QHS (C15H22O5) is a novel antimalarial drug isolated from Chinese herb Artemisia annua L in 1972. Structural studies by chemical analysis, X-ray single-crystal diffraction and other spectroscopic me- thods showed that QHS is a sesquiterpene lactone with a peroxide group (Fig. 1)[1]. In the past few decades, great achievements have been acquired in search for the mechanism of action of QHS[2~5]. Its unique endoperoxy bridge has attracted worldwide attention. Due to … 相似文献
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1INTRODUCTION Puerarin(4?,7-dihydroxy-8-β-D-glucosylisoflavo ne),whose chemical structure is shown in Fig.1,is a C-glycoside compound.It is present in a large amount of active components of Puerariae radix,a com-monly used Chinese herb,which exerts sedative and antipyretic actions and is often used to treat influ-enza,wrist stiffness and headache[1].A number of investigations were carried out internationally to iden-tify the physiological activities of puerarin such as antiproliferative… 相似文献
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理解等径圆球密堆积的性质和特点是学习金属晶体结构和性质的基础,密堆积中的空隙问题对学习和理解离子晶体的结构和性质非常重要。但晶体结构的多样性和复杂性,导致这部分内容成为结构化学课程中讲解和学习的一个难点问题。本文将以A1,A2,A3这三种最常见的密堆积结构为例,详细介绍一种利用质心分数坐标计算推导密堆积结构中四面体和八面体空隙中心的方法,以及如何通过坐标计算求解中心到顶点的距离和中心到堆积球面的最短距离。与立体几何方法相比较,质心分数坐标法不仅更加简洁易学,而且更有助于理解空隙在晶胞中的位置和分布问题。 相似文献
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4-甲基-6-羟基嘧啶与硝酸钴在乙醇溶液中反应,制得氢键连接的超分子配合物[Co(C~5H~6N~2O)~2(H~2O)~4]·(NO~3)~2。该化合物的结构已测定,晶体属于单斜晶系,空间群为C2/m,晶胞参数a=1.9853(4)nm,b=0.7601(5)nm,c=0.6539(13)nm,β=100.93(3)°,Z=2,最终偏离因子R=0.053。每一个结构单元中Co原子与两个4-甲基-6-羟基嘧啶和四个水分子配位,配位的水又通过氢键与硝酸根结合,同时嘧啶环上的羟基又与相邻结构单元中的嘧啶环上的未配位的N形成氢键,因而就形成了二维网状的超分子化合物。我们采用PM3半经验法计算表明配体4-甲基-6-羟基嘧啶中两个N原子的净电荷分布不同,因而配位能力不同,只有处在羟基邻位的N原子参与了配位。 相似文献
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二苯醚的势能面与构象研究 总被引:1,自引:0,他引:1
聚苯醚是具有多元重复氧桥结构的化合物。对这类体系的构象研究是一个很有意义的课题,如最简单的聚苯醚——二苯醚,文献中已提出三种不同的构象模型。Smyth等人认为,二苯醚中两苯环都垂直于C-O-C平面,即θ=φ=90°(见图1,θ,φ分别为两个苯环与C-O-C平面的夹角)。Sutton等人根据Pauling的假设认为,二苯醚中两个苯环共平面,即θ=φ=0。这样氧原子上孤对电子可参与共轭,使分子趋于稳定。Higgasi等人利用键矩加合规则,假定C-O-C键角为118°,计算了2,4,二取代甲基二苯醚及2,4,二取代碘 相似文献