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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 9: French-German Session: Simulation Methods and Modeling of Soft Matter I

CPP 9.2: Vortrag

Montag, 9. März 2026, 15:30–15:45, ZEU/LICH

THz Pump Pulse Drives Nonlinear H-bond Dynamics in Liquid Water — •Philipp Schienbein — Lehrstuhl für Theoretische Chemie II, Ruhr-Universität Bochum, 44780 Bochum, Germany — Research Center Chemical Sciences and Sustainability, Research Alliance Ruhr, 44780 Bochum, Germany

Light-matter interactions are central to processes in nature, chemical engineering, and fundamental research. Of particular interest is the frequency-dependent excitation of molecular systems by incident light. Here, we present machine-learning-accelerated molecular dynamics simulations of water subjected to an intense, monochromatic THz pump pulse, generating a total of 32 ns of trajectory data. The light pulse is explicitly modeled via a time-dependent external electric field, extending our previous framework for field-driven machine learning MD simulations, allowing us to observe the excitation in realtime. Our simulations reproduce key experimental observables, including transient dichroism and birefringence, and reveal that the pulse transiently modulates hydrogen-bond dynamics: H-bonds become markedly shorter-lived compared to unperturbed bulk water. This response is nonlinear, ruling out pure heating and resolving the experimental controversy. These results demonstrate that our machinery to incorporate electric fields in machine learning MD simulations can directly connect microscopic dynamics with measurable observables, further paving the way to controlling water dynamics - and potentially chemical reactivity - through tailored light pulses, a long-standing goal in chemistry.

Keywords: machine learning; molecular dynamics; light--matter interaction; vibrational spectroscopy; electric fields