Semiconductor Nanocrystals, Gold Nanostructures, Toxic Metals in the Environment

在计算方面，我的研究计划试图对(I)半导体纳米晶体、(Ii)金纳米结构和(Iii)环境中的有毒金属的性质进行建模，从而了解它们的性质。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成键的衡量标准，以及(Ii)获得作为电子密度的直接泛函的动能的准确表达式。对于基态计算，我们主要使用密度泛函理论(DFT)的Kohn-Sham公式，包括梯度修正泛函和混合泛函。对于激发态的计算，我们主要使用含时间的密度泛函理论(TD-DFT)和长程修正泛函。对于有限温度计算，我们主要使用Born-Oppenheimer分子动力学(BUMD)。 配体钝化半导体纳米晶(NCS)，又称量子点，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，就形成了电子-空穴对，如果它能被分离，就能产生电流。由于量子限制，较小的NC具有较大的带隙，可以更好地利用更高能量的光子。我们目前的重点是用Te取代Se或用Cu2取代Cd的CdSe纳米晶体及其相关结构。金纳米结构具有与大块金属非常不同的特性。我们确定了螺旋金纳米棒(包括裸的和有吸附分子的)的稳定性，并将它们与替代的致密和笼状结构进行了比较。我们目前的重点是螺旋金纳米棒的光电性质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，我们目前的重点是砷。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。人们对有机形态以及它们与无机土壤颗粒结合的方式知之甚少。

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.