Semiconductor Nanocrystals, Gold Nanostructures, Toxic Metals in the Environment

在计算方面，我的研究项目旨在建立模型，从而了解(i)半导体纳米晶体，（ii）金纳米结构，以及（iii）环境中的有毒金属的特性。在理论方面，我的研究计划寻求(i)检查量子势作为反应性和键合的度量，（ii）获得动能的精确表达式，这是电子密度的直接函数。对于基态计算，我们主要使用密度泛函理论（DFT）的Kohn-Sham公式，包括梯度校正泛函和混合泛函。对于激发态计算，我们主要使用具有远程修正泛函的时变密度泛函理论（TD-DFT）。对于有限温度计算，我们主要使用Born-Oppenheimer分子动力学（BOMD）。******配体钝化半导体纳米晶体（nc），也称为量子点，在包括光伏器件在内的许多领域都有应用。当能量大于带隙的光子被吸附时，就会形成电子-空穴对，如果能将其分离，就会产生电流。由于量子约束，较小的NC具有较大的带隙，可以更好地利用高能量光子。我们目前的重点是CdSe纳米晶体和相关结构，其中Se被Te取代或Cd被Cu2取代。金纳米结构具有与大块金属非常不同的性质。我们建立了螺旋金纳米棒的稳定性（包括裸的和吸附分子的），并将它们与其他紧凑结构和笼状结构进行了比较。我们目前的研究重点是螺旋金纳米棒的光电特性及其作为催化剂和生物传感器的手性应用。对于环境中的有毒金属，我们目前关注的是砷。砷以无机和有机两种形式存在，可通过生物地球化学过程相互转化。人们对有机形式以及它们与无机土壤颗粒结合的方式知之甚少。我们正在研究有机砷和氧化铁（氧合）配合物的性质，以及针铁矿表面的有机砷。******反应性和成键是化学的核心，尽管已经建立了电子密度的拉普拉斯函数和电子定位函数等方法，但其他方法可以提供重要的新见解。在这方面，我们计划研究量子势，它是电子密度的直接函数。在DFT的Kohn-Sham公式中，动能（通过N个单电子轨道）作为？但是缩放是非线性的。我们计划建立一个精确的直接（无轨道）动能泛函

On the computational side, my research program seeks to model and thereby understand the properties of (i) semiconductor nanocrystals, (ii) gold nanostructures, and (iii) toxic metals in the environment. On the theoretical side, my research program seeks to (i) examine the quantum potential as a measure of reactivity and bonding and (ii) obtain an accurate expression for the kinetic energy that is a direct functional of the electron density. For ground state calculations we primarily use the Kohn-Sham formulation of density functional theory (DFT) with both gradient-corrected and hybrid functionals. For excited state calculations we primarily use time-dependent density functional theory (TD-DFT) with long-range corrected functionals. For finite temperature calculations we primarily use Born-Oppenheimer molecular dynamics (BOMD). ******Ligand-passivated semiconductor nanocrystals (NCs), also called quantum dots, have applications in many areas including photovoltaic devices. Upon adsorption of a photon with energy greater than the band gap, an electron-hole pair is formed and, if it can be separated, an electric current can be generated. Due to quantum confinement, a smaller NC has a larger band gap which can make better use of higher energy photons. Our current focus is on CdSe nanocrystals and related structures in which Se is replaced by Te or Cd is replaced by Cu2. Gold nanostructures have properties which are very different from those of the bulk metal. We established the stability of helical gold nanorods (both bare and with adsorbed molecules) and compared them to alternative compact and cage structures. Our current focus is on the optoelectronic properties of helical gold nanorods and their chiral applications as catalysts and biosensors. For toxic metals in the environment, our current focus is on arsenic. Arsenic exists in both inorganic and organic forms that can be interconverted by biogeochemical processes. Less is known about the organic forms and the ways in which they bind to inorganic soil particles. We are examining the properties of organic arsenic and iron-(oxyhydr) oxide complexes, and organic arsenic on goethite surfaces.******Reactivity and bonding are at the heart of chemistry and, although measures such as the Laplacian of the electron density and the electron localization function have been established, other measures could provide important new insights. In this regard, we plan to examine the quantum potential, which is a direct functional of the electron density, ?. In the Kohn-Sham formulation of DFT, the kinetic energy is obtained accurately (via N one-electron orbitals) as an indirect functional of ? but the scaling is nonlinear. We plan to construct an accurate direct (orbital-free) kinetic energy functional.**