First principles simulations of electronic spectroscopy for larger molecules

为了详细了解复杂反应中涉及的分子结构，例如在生物背景下，能够解释各种光谱测量是至关重要的。对于包含多个过渡金属原子的体系，可行的光谱包括共振拉曼光谱、紫外可见吸收光谱、圆二色谱、磁性圆二色谱、电子顺磁共振、X射线近边吸收、X射线发射、穆斯堡尔谱、XPS、核磁共振和各种时间分辨泵浦-探测技术。对光谱的解释是一个复杂的过程，目前通常是基于与已知光谱的相似性匹配和使用简单的模型。对光谱的解释，也许更重要的是，光谱所隐含的系统的(结构)表征，可以得到可靠的第一原理理论模拟的很大帮助，这是这一提议的主题。在过去，我们开发了精确模拟小分子电子光谱的技术。其中的关键部分包括从精确的耦合团簇电子结构计算中提取所谓的振子模型参数，以及利用非绝热量子波包动力学研究多表面上量子核运动的演化。关键的挑战是将我们的方法推广到更大的系统中。我们计划将我们的方法纳入最先进的ORCA电子结构程序中，该程序是由MPI Mulheim an der Ruhr的Frank Neese小组开发的，并利用局部关联，特别是已应用于50-100个原子的系统的自然轨道对技术。此外，ORCA允许我们方便地结合相对论效应，特别是自旋-轨道耦合，这是模拟重要光谱性质的关键因素。ORCA将被推广到计算振动模型参数，而非绝热动力学的模拟则使用德国海德堡Meyer小组开发的广泛使用的多组态依赖于时间的Hartree(MCTDH)程序。

To gain a detailed understanding of molecular structures involved in complicated reactions, e.g. in a biological context, it is vital to be able to interpret a variety of spectroscopic measurements. For systems involving multiple transition metal atoms, viable spectroscopies include Resonance Raman, UV-VIS absorption, circular dichroism, magnetic circular dichroism, electron paramagnetic resonance, X-Ray near edge absorption, X-Ray emission, Mossbauer, XPS, NMR, and various time-resolved pump-probe techniques. The interpretation of spectra is a complicated process, and is currently often based on matching similarities to known spectra, and the use of simple models. The interpretation of the spectra, and perhaps even more importantly, the (structural) characterization of the system implied by the spectroscopy, can be greatly aided by reliable first principles theoretical simulations, the subject of this proposal. In the past we have developed technology to accurately simulate electronic spectroscopy for small molecules. The key ingredients involve the extraction of so-called vibronic model parameters from accurate coupled cluster type electronic structure calculations, and the evolution of quantum nuclear motion on multiple surfaces using non-adiabatic quantum wave packet dynamics. The key challenge is to generalize our methodologies to be applicable to larger systems. We plan to incorporate our methodology in the state-of-the-art ORCA electronic structure program, developed in the group of Frank Neese at MPI Mulheim an der Ruhr, and to capitalize on local correlation, in particular pair natural orbital techniques, which have been applied to systems as large as 50-100 atoms. In addition ORCA allows us to conveniently incorporate relativistic effects, in particular spin-orbit coupling, and this is a vital ingredient to simulate important spectroscopic properties. ORCA will be generalized to compute vibronic model parameters, while simulation of non-adiabatic dynamics is pursued employing the widely used Multiconfiguration Time-Dependent Hartree (MCTDH) package, developed in the Meyer group in Heidelberg, Germany.