Mixed Quantum/Semiclassical studies of spectroscopy and dynamics

在这个由化学学部化学理论、模型和计算方法项目资助的项目中，俄勒冈大学的Jeffrey A. Cina教授正在开发理论方法，用于模拟和解释基于吸光低温材料的随时间激光测量。基于分子的方法，接近量子力学行为，使得尽管这些系统很复杂，但仍有可能进行有效的计算。这种方法还允许根据运动来解释这些过程，很容易可视化，参与的分子和原子。正在发展的理论框架被称为固定振动基/高斯浴描述。为了模拟光谱信号，它以微扰形式发展，相对于几个外部激光脉冲的电场强度。该理论描述了多体化学系统的微观动力学，根据一组物理驱动的时间相关参数，与直接基集展开所需的线性系数集合相比，这些参数的数量较少。最初的应用是将共振驱动的小分子目标嵌入到稀有气体宿主晶体中。这类系统显示出许多凝聚相化学动力学的一般特征，同时由于在低温下量子力学效应的突出，并且适合混合量子/半经典处理，因此具有挑战性。计算信号的质量正在通过与广泛的实验数据和更多计算密集的理论结果（包括多配置时间相关的Hartree计算）进行比较来评估。

In this project funded by the Chemical Theory, Models and Computational Methods program of the Chemistry Division, Professor Jeffrey A. Cina of the University of Oregon is developing theoretical methods for simulating and interpreting time-dependent laser-based measurements of low-temperature materials that absorb light. The molecular-based approach, that approximates the quantum mechanical behavior, makes it possible to carry out efficient calculations despite the complexity of these systems. This method also allows the interpretation of these processes in terms of motion, easily visualized, of the participating molecules and atoms.The theoretical framework under development is termed a fixed vibrational basis/Gaussian bath description. For the purpose of simulating spectroscopy signals, it is being developed in perturbative form with respect to the electric field strengths of several external laser pulses. The theory describes the microscopic dynamics of many-body chemical systems in terms of a physically motivated set of time-dependent parameters that are small in number compared with the collection of linear coefficients that are required in a direct basis-set expansion. Initial applications are being made to resonantly driven small-molecule targets embedded in rare-gas host crystals. Systems of this kind display many generic features of condensed-phase chemical dynamics, while being both challenging, due to the prominence of quantum mechanical effects at cryogenic temperatures, and amenable to a mixed quantum/semi-classical treatment. The quality of the calculated signals is being assessed by comparison with extensive experimental data and more computationally intensive theoretical results, including multi-configuration time-dependent Hartree calculations.