New Tools and their Application for the study of nonadiabatic processes influenced by conical intersections

David Yarkony得到了化学部理论、模型和计算化学计划颁发的奖项的支持，该奖项旨在开发一种处理势能表面上锥形交点的新方法。描述电子势能面，包括锥形相交和态间相互作用，对于成功模拟非绝热过程是至关重要的。将锥形交点并入“拟合势能面”是一项具有挑战性的任务。在通常使用的称为从头算直接动力学或动态动力学的非绝热动力学方法中，通过根据需要直接从从头算电子结构计算中获得电子结构信息来绕过这个问题。目前，考虑到这些电子结构计算固有的高成本，在从头算非绝热直接动力学中，人们经常被迫牺牲电子波函数的精度来换取评估的速度。PI研究组开发的方法避免了这一瓶颈，从非局部准非绝热哈密顿量HD(‘Fit’哈密顿量)获得电子结构数据，该哈密顿量可靠地近似用于构建它的高质量从头算电子结构数据。这种HD准确地定位了锥形相交接缝、局部极小点、鞍点和离解渐近线，并再现了锥形相交的局部地形。分子在其中无辐射地改变其电子态的非绝热过程，即不吸收或发射光子，与能量存储、视觉和光化学等基本领域密切相关。锥形交点，即两个(或更多)电子势能面与双(或更高阶)锥体地形的交点，曾经被认为是一个神秘的理论概念，现在被认为在非绝热过程中发挥着关键作用。基于HD的电子结构设备正被连接到现有的直接动力学程序中，并提供给广泛的科学界。光电子能谱仪对它特别感兴趣。光电子能谱是研究分子中非绝热相互作用的有价值的工具。本科生和研究生都参加了这项研究项目，在开发和实施计算化学中的二元化方法方面获得了宝贵的培训。

David Yarkony is supported by an award from the Theory, Models and Computational Chemistry program in the Chemistry Division to develop a novel method of treating conical intersections on potential energy surfaces. Characterization of the electronic potential energy surfaces, including conical intersections and inter-state interactions is essential to the successful simulation of nonadiabatic processes. The incorporation of conical intersections into "fit" potential energy surfaces is a challenging task. In the commonly used nonadiabatic dynamics method known as ab initio direct dynamics or dynamics on the fly, this problem is circumvented by obtaining the electronic structure information directly from ab initio electronic structure calculations as required. At present, given the intrinsically high cost of these electronic structure calculations, in ab initio nonadiabatic direct dynamics, one is routinely forced to trade off accuracy of the electronic wave functions for speed of evaluation. The approach developed in the PI's research group avoids this bottleneck, obtaining the electronic structure data from a non-local quasi-diabatic Hamiltonian Hd (the 'fit' Hamiltonian) that reliably approximates the high quality ab initio electronic structure data used to construct it. This Hd correctly locates conical intersection seams, local minima, saddle points, and dissociation asymptotes, and reproduces the local topography of a conical intersection.Nonadiabatic processes in which molecules change their electronic states radiationlessly, that is, without absorbing or emitting a photon, are intimately involved in such essential areas as energy storage, vision and photochemistry. Once routinely dismissed as an arcane theoretical notion, conical intersections, i.e. points of intersection of two (or more), electronic potential energy surfaces with the topography of a double (or higher order) cone, are now understood to play a key role in nonadiabatic processes.The Hd based electronic structure apparatus is being interfaced into existing direct dynamics procedures and made available to a broad scientific community. It is of particular interest to photoelectron spectroscopists. Photoelectron spectroscopy is a valuable tool in accessing nonadiabatic interactions in molecules. Both undergraduate and graduate students take part in this research project, gaining valuable training in developing and implementing sophosticated methods in computational chemistry.