Connected by voids: Interactions and screening in sparse matter
Connected by voids: Interactions and screening in sparse matter
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通过空隙连接：稀疏物质中的相互作用和筛选
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发表时间：
2012
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通讯作者：
K. Berland
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作者：
K. Berland
利用理论和计算，我们研究纳米级系统的结构和电子特性，其中低密度区域对于响应和功能很重要。具有这种性质的材料称为稀疏物质。例子包括有机分子的组装和石墨等层状结构。使用密度泛函理论 (DFT) 和交换关系的范德华密度泛函 (vdW-DF) 解释来研究分子晶体中的结合和表面上的物理吸附。我们检查高对称性分子晶体（六胺、十二面体、立方烷、C60、石墨）的结合特性，因为它们可以直接分析结合性质。我们发现，vdW-DF 描述了一种非局部吸引力，与电势对描述中常见的 1/r6 形式相比，这种非局部吸引力在较短的距离下显着增强。研究了腺嘌呤、苯和 C60 在石墨烯上的结合。阐明了非局部 vdW-DF 相关性的几个属性，例如对几何形状、长度尺度和交换伴侣的作用的敏感性。研究了H2和苯在Cu(111)上的吸附。我们发现苯会影响表面状态，并且波纹足够小以使其能够对表面状态介导（SSM）相互作用做出反应。在所有情况下，vdW-DF 计算的结果与实验观察结果相比较。
Cu(111) 等贵金属表面具有支持二维电子气 (2DEG) 的金属肖克利表面态。这种表面状态被认为在分子自组装中发挥着至关重要的作用。使用 DFT，我们研究这个表面
状态以及外部场和物理吸附分子如何影响其特性。为了帮助我们的研究，我们开发了一种方法来增强基于平板的表面计算
州。我们还研究了苯在 Cu(111) 上的自组装，除了直接的范德华相互作用之外，我们还包括 SSM 相互作用的简单分析表达式。所得的结合曲线具有两个单独的最小值，与测量的覆盖层相的周期性一致。
最后，我们绘制了与 AlN/GaN 异质结构的联系。 In analogy to sparse matter, they exhibit wide regions of low conduction electron density.与这些耗尽区相关的是支持 2DEG 的反型层。这种电荷重新分布是由源自内在极化的内部场引起的。使用定制的薛定谔-泊松解算器研究这些结构。开发了一种消除引线内部场的系统设计策略，以帮助设计基于垂直于界面的传输的器件。
Using theory and computations, we study structural and electronic properties of nanoscale systems where regions of low density are important for response and function. Materials with such properties are called sparse matter. Examples include assemblies of organic molecules and layered structures like graphite. Binding in molecular crystals and physisorption onto surfaces is studied using density-functional theory (DFT) with a van der Waals density functional (vdW-DF) account of exchange-orrelation. We examine binding properties of molecular crystals of high symmetry (hexamine, dodeacahedrane, cubane, C60, graphite) as they allow straightforward analysis of binding nature. We find that vdW-DF describes a non-local attraction that is significantly enhanced at shorter separations compared to the 1/r6 form common in pair-potential descriptions. The binding of adenine, benzene, and C60 on graphene are studied. Several properties of the non-local vdW-DF correlation is elucidated, like sensitivity to geometry, length-scales, and role of exchange companion. Adsorption of H2 and benzene on Cu(111) is studied. We find that benzene affects the surface state and that the corrugation is small enough to allow it to react to surface-state mediated (SSM) interactions. In all cases, the results of vdW-DF calculations compare well to experimental observations.
Noble metal surfaces like Cu(111) harbor a metallic Shockley surface state that supports two-dimensional electron gas (2DEG). This surface state is believed to play a crucial role in the self-assembly of molecules. Using DFT, we study this surface
state and how an external field and physisorbed molecules influence its properties. To aid our study, we developed a method to enhance slab-based calculations of surface
states. We also investigate the self-assembly of benzene on Cu(111), where we include a simple analytical expression for the SSM interaction in addition to the direct van der Waals interactions. The resulting binding curves have two separate minima that coincide with the periodicity of the measured overlayer phases.
Finally, we draw a link to AlN/GaN heterostructures. In analogy to sparse matter, they exhibit wide regions of low conduction electron density. Associated with these depletion regions are inversion layers supporting 2DEGs. This charge redistribution arise from internal fields originating in intrinsic polarization. These structures are studied using a custom-built Schrodinger-Poisson solver. A systematic design strategy to remove the internal fields in the leads is developed to aid the design of devices based on transport perpendicular to the interfaces.