Geometry of the transition state in the driven dynamics of molecular and spintronic systems

在许多物理和化学系统中，系统在不同状态之间发生转变。人们对反应的机理、如何发生反应、反应速度，特别是控制反应的可能性非常感兴趣。过渡态理论(TST)可以定性和定量地描述活化反应。近年来，一个越来越受关注的领域是依赖时间的系统，它由噪声和/或外场驱动，因为它们允许人们主动控制反应速度和路径。TST的时间相关扩展能够准确地描述这类驱动系统，但到目前为止，所发展的方法仅限于简单的一维模型系统。该项目的目标是开发可应用于具有有限反应物盆地和多自由度的现实系统的方法，特别是允许准确地描述依赖时间的、受驱动的和高维激活系统的反应动力学。为此，定义和构造一个合适的、与时间相关的高维分割面是第一个目标，该分割面在任何时候都唯一地分离反应物和产物。第二个目标是将所开发的方法应用于化学和物理领域，例如，铁磁体中的LiCN异构化反应和自旋扭矩切换。对于这些体系，我们希望通过施加适当的外部驱动来全面而准确地描述依赖于时间的反应动力学，确定各自的反应速率，并控制反应路径。

Transitions of systems between different states take place in many physical and chemical systems. The mechanism, how a reaction takes place, the reaction rate, and in particular possibilities to control the reaction are of high interest. Transition state theory (TST)allows to describe activated reactions qualitatively as well as quantitatively. A field of growing interest over the recent years are time-dependent systems which are externally driven by noise and/or external fields, because they allow one to actively control the reaction rates and pathways. Time-dependent extensions of TST are capable of exactly describing such driven systems, however, so far, the developed methods are restricted to simple, one-dimensional model systems. The aim of the project is the development of methods which can be applied to realistic systems with finite reactant basins and many degrees of freedom, and, in particular, allow to exactly describe the reaction dynamics of time-dependent, driven, and high-dimensional activated systems. For this purpose, it is the first goal to define and construct an appropriate, time-dependent and high-dimensional dividing surface which uniquely separates reactants and products at all times. A second goal is the application of the developed methods to the fields of chemistry and physics with examples including, e.g., the LiCN isomerization reaction and spin-torque-switching in ferromagnets. For these systems we want to describe globally and exactly the time-dependent reaction dynamics, determine the respective reaction rates, and control the reaction pathways by applying an appropriate external driving.