Accurate Nonadiabatic Dynamics at Conical Intersections in Nanomaterials

在这项由化学理论、模型和计算方法计划资助的项目中，密歇根州立大学的本杰明·G·莱文教授正在开发新的计算方法来模拟半导体纳米材料中的非辐射复合。非辐射复合是将电子能量转换为热能的基本过程，因此限制了太阳能转换、光发射和其他应用的效率。正在开发的方法提供了这一过程的逐个原子、逐个电子的机械图，从而为未来材料的设计提供了信息。具体地说，Levine团队正在应用这些新的理论模型来阐明电子激发硅纳米颗粒的动力学，这种纳米颗粒有望成为固态显示器、生物成像和固态激光的发光体。Levine小组还与当地高中教师合作开发高中计算化学服务器(HiSoCCS)，它通过一个用户友好的基于网络的界面免费提供研究级计算化学能力。密歇根州高中免费提供HiSoCCS和相关课程材料。Levine小组的方法是基于这样的假设：锥形交叉点，即电子态之间的简并点，是由材料中的缺陷引入的，并且这些交叉点为非辐射复合提供了有效的途径。一种模拟锥形交叉口附近动力学的新的全量子力学方法--绝热表面上的非绝热高斯近似正在发展之中。DGA波函数ansatz被设计用来处理锥形交叉处发生的一阶和二阶导数非绝热耦合中的奇异性。DGA方法正在高性能并行计算机上实现，由此产生的软件将免费提供给其他科学家。这项工作的更广泛影响包括：a)开发了一种新的非绝热分子动力学方法，能够准确地模拟大范围的非辐射过程，b)新的开源软件，用于模拟锥形交叉点附近的动力学，c)对硅纳米材料中的非辐射复合有更深的理解，以及d)将研究分数计算纳入高中科学课程的新工具和材料。

In this project funded by the Chemical Theory, Models, and Computational Methods program, Professor Benjamin G. Levine of Michigan State University is developing new computational methods to model non-radiative recombination in semiconductor nanomaterials. Non-radiative recombination is a fundamental process that converts electronic energy to heat, thus limiting the efficiencies of devices for solar energy conversion, light emission, and other applications. The methods being developed provide an atom-by-atom, electron-by-electron mechanistic picture of this process, thus informing the design of future materials. Specifically, the Levine group is applying these new theoretical models to elucidate the dynamics of electronically excited silicon nanoparticles, which show promise as light emitters for solid state displays, biological imaging, and solid state lasers. The Levine group is also working with local high school teachers to develop the High School Computational Chemistry Server (HiSoCCS), which freely serves research-grade computational chemistry capability via a user-friendly web-based interface. HiSoCCS and associated curricular materials are made available for free to Michigan high schools. The Levine group's approach is based on the hypothesis that conical intersections, points of degeneracy between electronic states, are introduced by defects in the material, and that these intersections provide efficient pathways for non-radiative recombination. A new fully quantum mechanical method for modeling dynamics near conical intersections, the diabatized Gaussians on adiabatic surfaces (DGAS) approximation, is being developed. The DGAS wave function ansatz is designed to handle singularities in the first- and second-derivative nonadiabatic couplings that occur at conical intersections. The DGAS method is being implemented for high performance parallel computers, and the resulting software will be made freely available to other scientists. The broader impacts of this work include: a) the development of a new nonadiabatic molecular dynamics method capable of accurately modeling a wide range non-radiative processes, b) new open source software for modeling dynamics near conical intersections, c) a deeper understanding of non-radiative recombination in silicon nanomaterials, and d) new tools and materials that incorporate research grade calculations into the high school science curriculum.