Simulation methods and models for state preparation, excitation energy transport, and relaxation in pigment-protein systems

波士顿大学的David Coker获得了化学系化学理论、模型和计算方法项目的奖励。Coker和他的研究小组开发了研究在强光（光激发）下分子材料中能量如何移动的方法。了解如何控制能量在这些材料中的流向以及到达那里的速度是设计新技术的核心，这些技术可以收集阳光，利用太阳的能量进行产生燃料的化学反应，促进用于传感和成像应用的物理过程，或者选择和监测用于量子计算的特定量子态的演变。这些研究有两个组成部分。第一个目标是了解如何操纵化学结构和成分，以实现工艺设计和控制。第二个目标是了解如何操纵光来选择特定的激发态过程并控制其路径。这项研究为可持续能源和信息科学的应用提供了新的基础理解，为这些应用提供了新的计算方法和模拟工具，用于设计新的材料和工艺，并通过研究经验项目培训研究生和博士后，激励本科生和高中生，为高技能劳动力的发展做出了重大贡献。该项目正在开发一个基于一般第一性原理的模拟框架，用于探索光收集系统中的激发能输运（EET）和弛豫机制。重点是色素-蛋白质复合物，它耗散电子激发，将吸收蓝光的天线发色团的能量向下转换为红色，用于收获网络和反应中心的能量传输和转导。超快、非线性光谱学是这些过程的实验研究的主力，理论建模在从这些实验中解开机理理解方面起着关键作用。正在开发的方法超越了现有的高度平均的经验方法，这些方法可以给出模糊的机制预测。新方法结合了局部固有结构和涨落的详细统计抽样，并使用精确的第一性原理激发态计算参数化了模型哈密顿量的系综。这些模型用于耗散量子动力学计算，直接计算非线性光谱信号。这些非绝热动力学方法被扩展到包含高频量子振动运动，这对于快速耗散大量电子能量至关重要，从而提高效率。时间相关的驱动场也被纳入到这些方法中，因此它们可以处理超越微扰理论的辐射-物质相互作用，从而能够描述强场和复杂的重叠光脉冲序列，这些光脉冲序列可以用来控制激发态动力学。预测是以详细的实验为基准的。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

David Coker of Boston University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry. Coker and his research group develop methods to study how energy moves in molecular materials that are under strong light (photo-excited). Understanding how to manipulate where the energy goes in these materials as well as how quickly it gets there is central to designing new technologies that can harvest sunlight, using the sun's energy to conduct chemical reactions that produce fuels, to promote physical processes used in sensing and imaging applications, or to select and monitor the evolution of specific quantum states used in quantum computing. There are two components to these studies. The first objective is to understand how to manipulate chemical structures and compositions to enable process design and control. The second objective is to understand how light can be manipulated to select specific excited state processes and control their pathways. This research is resulting in new fundamental understanding for sustainable energy and information science applications, providing new computation methods and simulation tools to be used to design new materials and processes for these applications, and contributing significantly to highly skilled workforce development by training graduate student and post-docs and inspiring undergraduate and high school student through research experience programs. This project is developing a general first principles based simulation framework for exploring mechanisms of excitation energy transport (EET) and relaxation in light harvesting systems. The focus is on pigment-protein complexes that dissipate electronic excitation to down convert the energy of blue light absorbing antenna chromophores to the red for energy transport and transduction in harvesting networks and reaction centers. Ultrafast, nonlinear spectroscopy is the workhorse for experimental studies of these processes and theoretical modeling plays a critical role in disentangling mechanistic understanding from these experiments. The methods being developed go beyond the existing highly averaged empirical approaches that can give ambiguous mechanistic predictions. The new approach incorporates detailed statistical sampling of local inherent structures and fluctuations and parameterizes ensembles of model Hamiltonians using accurate first principles excited state calculations. These models are used in dissipative quantum dynamics calculations to directly compute nonlinear spectroscopy signals. These non-adiabatic dynamics methods are extended to incorporate high frequency quantum vibrational motions critical for dissipating large amounts of electronic energy quickly, promoting efficiency. Time dependent driving fields are also incorporated into these methods so they can treat the radiation – matter interaction beyond perturbation theory enabling the description of strong fields and complex sequences of overlapping light pulses that can be used to control excited state dynamics. Predictions are being benchmarked against detailed experiments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.