First-principles studies of time-resolved nonlinear optical spectroscopy signals

俄勒冈大学的Jeffrey A. Cina得到化学学部化学理论、模型和计算方法项目的支持，开发和实施理论方法，使凝聚态分子系统中两类时间分辨光谱信号的第一性原理计算和解释成为可能。在一个领域，中国和他的同事们正在努力预测基于从头计算共振耦合电子势能表面的超快相相干多维电子能谱测量结果。在这个方向上的进展依赖于一个新理论的框架和实现，该理论基于系统地将所有分子内和分子间的振动自由度划分为与相关电子跃迁强耦合的自由度和弱耦合或不耦合的自由度。另一个理论研究领域涉及进一步发展和应用混合量子/半经典方法，用于模拟和解释嵌入在低温晶体中的小分子的时间分辨光谱信号。加州大学欧文分校的V. Ara Apkarian及其同事正在进行实验研究，这些系统的一个基本特征是存在少量相对高频的振动自由度，我们的理论对其动力学进行了严格的数值处理，并与大量可适应半经典近似的低频振动相结合。这项工作通过教育和培训研究生和本科生与实验研究者合作，构建和解决复杂的理论和计算问题，具有更广泛的影响。科学影响包括计算工具的发展，适用于分子科学中广泛感兴趣的重大问题。我们的理论研究的两个方面都有可能为自然和人工光合能量收集以及基于分子的量子信息处理领域的进步做出贡献。

Jeffrey A. Cina of the University of Oregon is supported by the Chemical Theory, Models and Computational Methods program in the Chemistry Division to develop and implement theoretical methods enabling the first-principles calculation and interpretation of two classes of time-resolved spectroscopic signals from condensed molecular systems. In one area, Cina and his coworkers are endeavoring to predict the results of ultrafast phase-coherent multidimensional electronic spectroscopy measurements based on the ab initio determination of resonantly coupled electronic potential energy surfaces. Progress in this direction relies on the framing and implementation of a new theory based on systematically partitioning all intra and intermolecular vibrational degrees of freedom into those that are strongly coupled to the relevant electronic transitions and those that are weakly coupled or not coupled. The other area of theoretical study involves the further development and application of a mixed quantum/semiclassical method for the simulation and interpretation of time-resolved spectroscopic signals from small molecules embedded in low-temperature crystals. An essential feature of these systems, which are under experimental study by V. Ara Apkarian and co-workers at UC-Irvine, is the existence of a small number of relatively high-frequency vibrational degrees of freedom, whose dynamics our theory treats numerically rigorously, coupled to a large number of lower-frequency vibrations amenable to semiclassical approximation. This work has a broader impact through the education and training of graduate and undergraduate students to frame and solve complex theoretical and computational problems in collaboration with experimental investigators. Scientific impacts include the development of computational tools applicable to significant problems of widespread interest in molecular science. Both aspects of our theoretical research have the potential to contribute to progress in the areas of natural and artificial photo-synthetic energy harvesting, and molecule-based quantum information processing.