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

Gregory Voth得到了理论和计算化学计划的资助，继续他对质心分子动力学(CMD)技术的理论发展，并将其应用于具有量子自由度的系统的凝聚相动力学领域的一些重要问题。CMD方法基于经典分子动力学技术计算Feynman路径积分质心的轨迹。然后用相空间Feynman路径积分质心密度对轨迹进行相关和统计加权。所得到的时间关联函数可以通过傅里叶变换关联到量子时间关联函数。因此，CMD允许通过类似于经典MD计算的数值工作来近似计算量子时间关联函数。将对几个应用程序进行调查。将讨论质子在水中的迁移以及溶剂化电子和水合电子的扩散传输。第二个研究领域涉及发展凝聚相系统的初值半经典动力学方法。这种方法将允许研究非平衡和非绝热过程，并处理“系统-浴缸”的非线性相互作用。最后，将对激活的量子动力学进行正式处理，以开发量子力学过渡态的新图景。多年来，人们对气相化学体系进行了研究，并发展了优秀的理论和计算技术来模拟它们的行为。最近，理论和计算方法正在发展，使得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，不能处理量子效应带来的额外复杂性。沃斯的研究解决了这种额外程度的复杂性，并建议开发计算方法，以允许处理包括各种量子自由度的凝聚相系统。

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.