First Principles Simulation Methods for Strong Field Dynamics

斯托尼布鲁克大学的Benjamin Levine教授获得了化学系化学理论、模型和计算方法项目的奖励，以开发界面化学动力学的分子水平模型。 激光被用于从先进制造到通信到医学的许多领域。强激光脉冲已经成为在短时间尺度上探测分子中电子-核运动的有力工具。 虽然激光在很短的时间内将大量能量引入分子，但随之而来的化学运动（动力学）是复杂的。 强激光场中的化学动力学很难用标准方法建模，因此需要更先进的模拟方法。 激光科学中的一个重要主题是激光准直。 在这个过程中，激光场从分子中取出一个电子，然后将该电子以高能量驱动回剩余的阳离子。 这种碰撞过程的可能结果包括散射，第二个电子的去除，以及高能量光包（光子）的发射。 重碰撞是基本的兴趣，并作为先进的测量与阿秒（一秒的五分之一）的时间分辨率和高空间分辨率的基础。 莱文小组将开发第一原理计算机模拟方法来建模。 这项工作将为理论化学界提供建模和解释强场激光实验的新理论工具。在这个过程中，未来的科学家，包括研究生和本科生，将接受化学，物理，高性能计算和数学方面的培训。 莱文教授计划组织一个国际研讨会，将促进对挑战理论家的化学问题建模的理论方法的讨论。 他将继续通过美国化学学会密歇根州立大学地方分会及其相关学生团体开展工作（青年化学家委员会，化学界女性），为年轻化学家提供领导机会和指导。Levine小组将开发一种混合的分析仪，其中完全多电子系统的电离最初通过时间相关构型相互作用（TD-CI）进行量子力学处理，但是在从分子分离时，被喷射的电子被半经典地处理。 这种新的方法来模拟电子动力学将耦合到多克隆在稠密流形的状态（MCDMS），一个非绝热分子动力学计划能够准确，有效地模拟耦合的电子-核动力学在电离过程中访问的连续电子状态。 由于这种组合的TD-CI/MCDMS方法将以完整的量子力学细节对整个电离/电离过程进行建模，因此它避免了对电离后系统初始状态的常见和潜在不准确的简化假设的需要。 这些新的方法将被应用于明确模拟电子和耦合电子核动力学的几个小分子照射下的强激光脉冲，该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准。

Professor Benjamin Levine of Stony Brook University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to develop molecular-level models of interfacial chemical dynamics. Lasers are used in many fields from advanced manufacturing, to communications, to medicine. Strong laser pulses have arisen as powerful tools for probing electron-nuclear motions in molecules on the short time scales. Though lasers introduce large quantities of energy into molecules in a very short time, the ensuing chemical motions (dynamics) are intricate. Chemical dynamics in strong laser fields are challenging to model with standard approaches, creating a need for more advanced simulation methods. An important motif in laser science is recollision. In this process, the laser field plucks a single electron from the molecule and then drives that electron back into the remaining cation at high energy. The possible outcomes of such recollision processes include scattering, the removal of a second electron, and the emission of a high energy packet of light (photon). Recollision is of fundamental interest and serves as the basis of advanced measurements with attosecond (one quintillionth of a second) time resolution and high spatial resolution. The Levine group will develop first-principles computer simulation methods for modeling recollision. The work will provide the theoretical chemistry community with new theoretical tools for modeling and interpreting strong-field laser experiments. In the process, future scientists, including graduate and undergraduate students, will be trained in chemistry, physics, high-performance computing, and mathematics. Professor Levine plans to organize an international workshop that will facilitate discussion about theoretical methods for modeling chemical problems that challenge theorists. He will continue to work through the Michigan State University local section of the American Chemical Society and its associated student groups (Young Chemists' Committee, Woman in Chemistry) to provide younger chemists with leadership opportunities and mentorship.The Levine group will develop a mixed ansatz, in which the ionization of the full many-electron system is initially treated quantum mechanically via time-dependent configuration interaction (TD-CI), but upon separation from the molecule the ejected electron is treated semiclassically. This novel approach to modeling electron dynamics will be coupled to multiple cloning in dense manifolds of states (MCDMS), a nonadiabatic molecular dynamics scheme capable of accurately and efficiently modeling coupled electron-nuclear dynamics in the continuum of electronic states accessed during ionization. Because this combined TD-CI/MCDMS approach will model the entire ionization/recollision process in full quantum mechanical detail, it avoids the need for common and potentially inaccurate simplifying assumptions about the initial state of the system after ionization. These novel methods will be applied to explicitly model the electron and coupled electron-nuclear dynamics of several small molecules under irradiation by strong laser pulses, enabling both validation of the accuracy of the new simulation methods and elucidation of the intricate electronic motions underlying the experimental observations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.