Theoretical and Computational Studies of Quantum Dynamical Processes in Condensed Matter

犹他大学的Gregory A. Voth教授得到了理论和计算化学项目的支持，在激发态反应动力学、表面化学和凝聚相过程方面进行理论研究。目前的重点是扩展和进一步发展质心分子动力学方法（CMD）。CMD方法是基于经典分子动力学技术计算费曼路径积分质心的轨迹。然后用相空间费曼路径积分质心密度对轨迹进行关联和统计加权。得到的时间相关函数可以通过傅里叶变换与量子时间相关函数相关联。因此，CMD允许用类似于经典MD计算的数值努力来近似计算量子时间相关函数。这些方法旨在了解质子在水环境中的输运和水合电子的模拟。正在开发的具体改进包括：(1)开发一种精确的数值算法来对CMD动力学进行修正，(2)结合质心动力学传播的半经典初始值表示，(3)使用高斯表示简化CMD方法，包括电子自由度的非绝热动力学，(4)包含非线性相关函数，(5)包含费米-狄拉克统计。复杂凝聚相系统中的质子转移是许多生物过程的基本方面，如植物的光合作用和动物的呼吸。对这些过程的完全理解目前还不存在，需要复杂的理论处理，能够解释电子的量子力学行为和质子的近乎经典的运动。这里开发的方法非常适合于与近乎经典的质子转移相关的动力学描述。进一步了解这些过程对于开发用于太阳能转换、碳封存和可能的生物启发的环境友好催化的仿生材料是必要的。类似的动力学对大气化学也很有兴趣，因为质子化的水团簇在高层大气中很丰富。通过培训研究生和研究生研究人员，研究也被传授给各个社区。

Professor Gregory A. Voth, of the University of Utah, is supported by the Theoretical and Computational Chemistry Program to perform theoretical studies on excited-state reaction dynamics, surface chemistry and condensed-phase processes. Current focus is on extending and further developing the centroid molecular dynamics method (CMD). The CMD method is based on computing trajectories of Feynman path integral centroids using classical molecular dynamics techniques. The trajectories are then correlated and statistically weighted with the phase space Feynman path integral centroid density. The resulting time correlation function can be related by Fourier transform to the quantum time correlation function. CMD therefore allows quantum time correlation functions to be approximately calculated with a numerical effort similar to a classical MD calculations. Such methods are aimed at understanding proton transport in aqueous environments and in the simulation of hydrated electrons. Specific improvements under development include: (1) the development of a numerically exact algorithm to provide corrections to the CMD dynamics, (2) the incorporation of the semiclassical initial value representation for centroid dynamics propagation, (3) simplifying the CMD approach using Gaussian representations, including nonadiabatic dynamics of the electronic degrees of freedom, (4) inclusion of nonlinear correlation functions, and (5) inclusion of Fermi-Dirac statistics.Proton transfer in complex condensed phase systems is a fundamental aspect of many biological processes such as photosynthesis in plants and breathing in animals. The complete understanding of these processes is currently absent and in need of sophisticated theoretical treatments that are capable of accounting for the quantum-mechanical behavior of electrons and the nearly classical motion of protons. Methods developed here are well suited for dynamical descriptions associated with nearly classical proton transfer. Further understanding of these processes is requisite to the development of biomimetic materials for solar energy conversion, carbon sequestration and possibly biologically inspired environmentally friendly catalysis. Similar dynamics are of interest to atmospheric chemistry since protonated water clusters are abundant in the upper atmosphere. Research is also imparted to various communities through the training of graduate and postgraduate researchers.