First Principles Simulation Methods for Strong Field Dynamics

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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.