若干低维体系的第一性原理研究

发布时间：2018-04-29 13:14

本文选题：第一性原理计算 + 电子阴离子化合物　；参考：《中国科学技术大学》2017年博士论文

【摘要】：随着密度泛函理论和计算机科学的发展,第一性原理计算的模拟准确度和应用范围大大提高,目前已成为物质科学领域不可或缺的研究手段。一方面,和实验上传统的"试错法"材料设计相比,基于第一性原理的材料设计方法可极大地降低新材料的设计成本,缩短其开发周期。另一方面,第一性原理计算不仅能给出材料本身的结构和性质特征,还能考察体系间的相互作用,为材料的性能及制备方法提供机理解释和理论指导。基于密度泛函理论的第一性原理计算,本论文研究了一些低维材料的几何构型和电子结构特征。主要包括以下几部分内容:第一章为第一性原理计算的理论基础简介。我们先简述基于波函数的量子化学方法,然后引入基于电荷密度的密度泛函理论,其中着重介绍密度泛函理论中交换关联泛函的发展脉络和方向,以及在弱相互作用体系中密度泛函的处理方法。此外,我们介绍一下常用的第一性原理软件包、基本的模拟原则及数据后处理的软件。本章最后,我们简单介绍一下与本论文中相关的扫描隧道显微镜(STM)图像模拟方法。第二章中我们介绍具有本征悬浮二维电子气体系的理论设计。研究的对象为一种新奇的材料,电子阴离子化合物,其内部具有周期性、化学计量比的非局域电子直接充当阴离子。这些阴离子电子分布在远离原子核的自由空间,受原子核的散射较弱。受新型二维电子阴离子化合物Ca2N的启发,我们先证明可通过体相剥离的方法制备出稳定的Ca2N单层材料,后证实其表面的阴离子电子会弥散在远离阳离子骨架的自由空间,形成悬浮的二维电子气。这些悬浮二维电子气的确能提供弱核散射的电子传输通道。但悬浮二维电子气十分的化学活泼,我们提议使用石墨烷对其范德华封装,理论设计出了大气环境下稳定的悬浮二维电子气体系。第三章研究了零维金属纳米颗粒的电子结构性质。我们发现Au75Pd25合金二十面体纳米颗粒中的孪晶结构诱导了表面晶格的膨胀,抬升了表面的d带中心。同时,合金中电荷由钯原子向金原子转移,使得表面金原子上的负电荷浓度升高。二者协同提升了实验上Au75Pd25二十面体纳米颗粒催化环己烷氧化的反应活性。第四章研究的是铜硫化合物材料界面处的电子结构性质。我们发现CU1.94S和CuS均具有合适的带隙,可作为光电响应的材料。在Cu1.94S(100)-cuS(100)异质结中,界面处的能带排布使得光生电子流向Cu1.94S端,而光生空穴则在CuS端聚集。同时,异质结的哑铃状构型能增强CuS高导电面与电极的接触。异质结的电子结构和几何构型共同促进了界面处电子空穴对的分离与传输,使其光电转化性能明显优于单独的Cu1.94S或CuS。第五章我们着重讨论磷与衬底间的相互作用。由于在电子器件和光电转化方面具有重大应用前景,二维磷结构是目前材料领域的热点,而研究的重点是选择合适的衬底进行少数层二维磷的生长。实验合作组首先在Au(111)表面合成出了蜂窝状的二维磷结构,我们计算表明实验上制备的二维磷是蓝磷的重构体。当实验上使用比金活泼的铜作为衬底时,在其表面只能观察到有序磷条纹的生成。计算表明Cu(110)和磷的作用很强,其表面生长的磷条纹是离散磷原子的吸附结构。最后,实验上利用碲原子修饰的Au(111)作为衬底进行蓝磷的外延生长。我们模拟发现,相比Au(111),蓝磷在碲修饰的Au(111)表面的吸附更弱,电荷转移更小,的确有利于制备准自由的二维蓝磷。综合来看,二维磷自身结构不像石墨烯那么强健,其外延生长需要那些活性较弱的基底,如金或其他适合的半导体。
[Abstract]:With the development of density functional theory and computer science, the simulation accuracy and application range of the first principle calculation have been greatly improved. At present, it has become an indispensable research means in the field of material science. On the one hand, compared with the traditional "trial and error" material design, the material design method based on the first principle can be greatly reduced. The design cost of low new material reduces its development cycle. On the other hand, the first principle calculation can not only give the structure and properties of the material itself, but also examine the interaction between the systems, provide the mechanism interpretation and theoretical guidance for the properties and preparation methods of the materials. The geometric configuration and electronic structure characteristics of some low dimensional materials are studied. The main contents are as follows: the first chapter is a brief introduction to the theoretical basis of the first principle calculation. First, we briefly describe the quantum chemical method based on the wave function, and then introduce the density functional theory based on the charge density, which focuses on the introduction of the density functional theory. In addition, we introduce the commonly used first principles software packages, basic simulation principles and data processing software. In this chapter, we give a brief introduction to the scanning tunneling microscope (STM) map related to this paper. In the second chapter, we introduce the theoretical design of an eigen suspended two-dimensional electron gas system. The object of this study is a novel material, an electron anionic compound, which has a periodic interior and a stoichiometric non local electron directly acting as an anion. These anion electrons are distributed in the free space far away from the nucleus. The scattering of the nucleus is weak. Inspired by the new two-dimensional electron anion compound Ca2N, we first prove that the stable Ca2N monolayer can be prepared by the method of body phase stripping, and then it is proved that the anionic electrons of the surface will disperse in the free space far away from the cation framework and form the suspended two-dimensional electron gas. Electron gas can indeed provide an electron transport channel with weak nuclear scattering. However, the suspension two-dimensional electron gas is very chemical active. We propose to use graphane for its van Edward package and theoretically design a stable suspended two-dimensional electronic gas system in the atmosphere. In the third chapter, the electronic structure properties of the null gold nanoparticles are studied. We find that the electronic structure properties of the null gold nanoparticles are studied. The twin structure in the Au75Pd25 alloy twenty surface nano particles induces the expansion of the surface lattice and the d band center of the surface. At the same time, the charge in the alloy is transferred from the palladium atom to the gold atom, which increases the negative charge concentration on the surface of the gold atoms. The two groups enhance the experimental Au75Pd25 twenty surface nanoparticles to catalyze the cyclohexane oxygen. The fourth chapter studies the electronic structural properties at the interface of copper and sulfur compounds. We found that both CU1.94S and CuS have appropriate band gaps and can be used as photoelectrical responses. In the Cu1.94S (100) -cuS (100) heterojunction, the band arrangement at the interface makes the photoelectrons flow to the Cu1.94S end, while the bare holes are at the CuS end. At the same time, the dumbbell shaped configuration of the heterojunction can enhance the contact between the CuS high conductivity surface and the electrode. The electronic structure and geometry of the heterojunction jointly promote the separation and transmission of the electron hole pair at the interface. The photoelectric conversion performance is obviously superior to the separate Cu1.94S or CuS. fifth chapters, and the interaction between the phosphorus and the substrate is emphatically discussed. The two dimensional phosphorus structure is a hot spot in the field of materials in the field of electronic and photoelectric conversion. The focus of the study is to select the suitable substrate for the growth of a few layers of phosphorus. The experimental cooperation group first synthesized the honeycomb like two-dimensional phosphorus structure on the surface of Au (111). Two dimensional phosphorus is a reconfiguration of blue phosphorus. When the active copper is used as a substrate in the experiment, the formation of ordered phosphorous stripe can only be observed on its surface. The calculation shows that Cu (110) and phosphorus are strong and the phosphorous stripe of its surface is the adsorption structure of the discrete phosphorus atom. Finally, the Au (111) modified by tellurium atom is used as the substrate. We found that the adsorption of blue phosphorus on the Au (111) surface modified by tellurium is weaker than that of Au (111), and the charge transfer is smaller. It is indeed beneficial for the preparation of quasi free two-dimensional blue phosphorus. A suitable semiconductor.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB30

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