Theoretical and Computational Studies of Quantum Dynamical Processes in Condensed Matter Systems

Gregory Voth获得了理论和计算化学项目的资助，继续他的质心分子动力学（CMD）技术的理论发展，并将其应用于具有量子自由度系统的凝聚相动力学领域的一些重要问题。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。几项申请将被调查。质子在水中的易位和溶剂化和水合电子的扩散输运将被处理。第二个研究领域涉及凝聚态系统的初值半经典动力学方法的发展。这种方法将允许研究非平衡和非绝热过程，以及处理非线性“系统浴”相互作用。最后，将对激活量子动力学进行正式处理，以发展量子力学过渡态的新图景。气相化学系统已经被研究了许多年，并且已经发展了优秀的理论和计算技术来模拟它们的行为。最近正在开发理论和计算方法，使处理更复杂的凝聚相系统成为可能。目前的大多数理论模型本质上都是经典的，无法处理量子效应带来的额外复杂性。Voth的研究解决了这个额外的复杂程度，并提出了设计用于处理包含各种量子自由度的凝聚相系统的计算方法的发展。

Gregory Voth is supported by a grant from the Theoretical and Computational Chemistry Program to continue his theoretical development of the Centroid Molecular Dynamics (CMD) technique, and to apply it to a number of important problems in the area of condensed phase dynamics of systems with quantum degrees of freedom. 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 calculation. Several applications will be investigated. Proton translocation in water and the diffusive transport of solvated and hydrated electrons will be treated. A second area of research involves the development of an initial value semiclassical dynamics approach for condensed phase systems. This approach would allow the study of both nonequilibrium and nonadiabatic processes, and treatment of nonlinear `system-bath` interactions. Finally, a formal treatment of activated quantum dynamics will be undertaken to develop a new picture of the quantum mechanical transition state. Gas phase chemical systems have been studied for a number of years, and excellent theoretical and computational techniques have been developed to model their behavior. More recently theoretical and computational methods are being developed that make it possible to treat more complex condensed phase systems. Most of the current theoretical models are classical in nature and cannot deal with the additional complications imposed by quantum effects. Voth's research addresses this additional degree of complexity and proposes the development of computational approaches designed to permit the treatment of condensed phase systems that include various quantum degrees of freedom.