NSF Young Investigator: Many Body Approaches for the Study of Photochemical Processes

John Stanton由理论和计算化学计划授予的NSF青年研究人员资助，开发和实施多体从头算分子轨道方法来研究光化学过程。该方法基于运动方程和Fock空间对电子基态的耦合团簇近似的推广。这项研究的具体目标包括：1)计算末态的约化密度矩阵、电子性质和解析能量导数的技术的理论表述和计算实现，这些技术由一类Fock空间方法参数化，这种方法允许自旋适应的、大小扩展的多体处理开壳态；2)扩展现有的运动方程方法，允许将这些方法应用于非绝热过程的计算；以及3)算法的设计，使这些理论方法适用于相对较大的系统。光化学往往会驱动许多决定平流层复杂化学的重要连锁反应，因为吸收太阳光子通常会导致光解。当前的重要问题是含氯化合物的光解和随后的光碎片化学，因为这些体系明确涉及导致极地平流层臭氧破坏的催化机制。斯坦顿对这些开壳分子的激发态的研究将有助于它们的理论表征和光谱技术的检测。他的研究还将有助于计算激发态的势能面，这些势能面可以用来模拟光解事件

John Stanton is supported by an NSF Young Investigator Grant from the Theoretical and Computational Chemistry Program to develop and implement many-body ab initio molecular orbital approaches to the study of photochemical processes. The approach is based on equation-of-motion and Fock space generalizations of the coupled-cluster approximation for electronic ground states. Specific aims of the research include: 1) the theoretical formulation and computational implementation of techniques for calculating reduced density matrices, electronic properties and analytic energy derivatives for final states parameterized by a class of Fock space methods that allow a spin-adapted, size-extensive, many-body treatment of open-shell states; 2) extensions of existing equation-of-motion methodology that will permit application of these methods to the calculation of nonadiabatic processes; and 3) the design of algorithms that will make these theoretical methods applicable to relatively large systems. Photochemistry tends to drive many of the important chain reactions that determine the complex chemistry of the stratosphere, as absorption of solar photons typically leads to photodissociation. Of current importance is the photolysis and subsequent photofragment chemistry of chlorine containing compounds, as these systems have unambiguously been implicated in catalytic mechanisms leading to destruction of ozone in polar stratospheric regions. Stanton's studies of excited states of these open-shell molecules will assist in their theoretical characterization and detection by spectroscopic techniques. His research will also contribute to the calculation of potential energy surfaces for excited states which can be used to simulate photodissociation events