Mixed Quantum/Semiclassical studies of spectroscopy and dynamics

在这个由化学系化学理论、模型和计算方法项目资助的项目中，Jeffrey A。俄勒冈州大学的Cina正在开发理论方法，用于模拟和解释吸收光的低温材料的基于时间的激光测量。 基于分子的方法近似于量子力学行为，使得尽管这些系统很复杂，但仍然可以进行有效的计算。这种方法也允许解释这些过程中的运动，很容易可视化，参与分子和原子。发展中的理论框架被称为固定振动基础/高斯浴描述。 为了模拟光谱信号的目的，它正在开发的微扰形式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，其依据是一组物理动机的时间相关参数，与直接基组展开所需的线性系数集合相比，这些参数的数量很少。 最初的应用是在稀有气体基质晶体中嵌入共振驱动的小分子靶。 这类系统显示出凝聚相化学动力学的许多通用特征，同时由于在低温下量子力学效应的突出而具有挑战性，并且可以进行混合量子/半经典处理。 通过与大量实验数据和计算密集的理论结果（包括多配置时间相关Hartree计算）进行比较，评估计算信号的质量。

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.