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Online Link：https://nationaltaiwanuniversity-zbh.my.webex.com/nationaltaiwanuniversity-zbh.my-tc/j.php?MTID=m0ab85f1d48c3edcd94d2db6df50fff8a
Meeting number： 2559 751 9111
Password： ZJfU2r7tfD2（95382778 for joining from the phone）
14:00-15:00 Prof. Jaeyoung Sung
Creative Research Initiative Center for Chemical Dynamics in Living Cells
& Department of Chemistry, Chung-Ang University, Seoul, Korea
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| Title：Transport Dynamics of Complex Fluids |
Thermal motion in complex fluids is a complicated stochastic process but ubiquitously exhibits initial ballistic, intermediate subdiffusive, and long-time diffusive motion, unless interrupted. Despite its relevance to numerous dynamical processes of interest in modern science, a unified, quantitative understanding of thermal motion in complex fluids remains a challenging problem. Here, we present a transport equation and its solutions, which yield a unified quantitative explanation of the mean-square displacement (MSD), the non-Gaussian parameter (NGP), and the displacement distribution of complex fluids. In our approach, the environment-coupled diffusion kernel and its time correlation function (TCF) are the essential quantities that determine transport dynamics and characterize mobility fluctuation of complex fluids; their time profiles are directly extractable from a model-free analysis of the MSD and NGP or, with greater computational expense, from the two-point and four-point velocity autocorrelation functions. We construct a general, explicit model of the diffusion kernel, comprising one unbound-mode and multiple bound-mode components, which provides an excellent approximate description of transport dynamics of various complex fluidic systems such as supercooled water, colloidal beads diffusing on lipid tubes, and dense hard disk fluid. This work presents an unexplored direction for quantitative understanding of transport and transport-coupled processes in complex disordered media.
References
[1] Song et al., Transport Dynamics of Complex Fluids, Proc. Nat. Acad. Sci. U.S.A.116, 12733 (2019).
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| 15:00-15:10 Break |
15:10-16:10 Prof. Tetsuya Taketsugu
Department of Chemistry, Faculty of Science, Hokkaido University; Institute for Chemical Reaction Design and Discovery (WPI-ICReDD), Hokkaido University, Sapporo, Japan
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| Title：Exploring photoreactions through on-the-fly molecular dynamics and reaction space projector techniques |
On-the-fly molecular dynamics (MD) serves as a powerful tool for shedding light on the mechanisms and dynamics of photochemical reactions. Our development of a surface hopping on-the-fly MD method integrates nonadiabatic transitions [1], paving the way for our recent studies on how intersystem crossing dynamics vary with the use of spin-diabatic versus spin-adiabatic potential energy surfaces [2]. In the case of stilbene (SB), we observe cis–trans photoisomerization around its central C=C bond upon ππ* excitation, leading to an ultrafast transition to the ground state for ππ*-excited cis-SB. This process was explored using femtosecond Raman spectroscopy and theoretical calculations to understand the vibrational motion changes post-excitation, unveiling the primary nuclear dynamics of ππ*-excited cis-SB [3]. Employing on-the-fly MD at the spin-flip TDDFT level for ππ*-excited cis-SB allowed us to closely replicate the experimental branching ratio between trans-SB and its by-product, DHP [4]. Moreover, we have identified the elusive, perpendicular intermediate common to stilbene photoisomerization through ultrafast Raman spectroscopy and computational analysis [5]. Introducing the reaction space projector (ReSPer) method marks a significant advancement; this technique constructs a reaction space from reference paths and projects trajectories into this space [6]. By extending ReSPer to cover photoreaction dynamics and applying it to SB's photoreaction, we've introduced the novel concept of a "multi-state energy landscape" that encompasses reaction subspaces of both ground and excited states. This innovation broadens the scope of ReSPer analysis, enabling its application across a wider array of molecules within a unified framework.
References
[1] T. Taketsugu, A. Tajima, K. Ishii, T. Hirano, Astrophys. J. 2004, 608, 323; Y. Ootani, K. Satoh, A. Nakayama, T. Noro, T. Taketsugu, J. Chem. Phys., 2009, 131, 194306.
[2] S. Wada, T. Tsutsumi, K. Saita, T. Taketsugu, J. Comput. Chem., 2024, 45, 552.
[3] S. Takeuchi, S. Ruhman, T. Tsuneda, M. Chiba, T. Taketsugu, T. Tahara, Science 2008,322, 1073.
[4] Y. Harabuchi, K. Keipert, F. Zahariev, T. Taketsugu, and M. S. Gordon, J. Phys. Chem. A 2014, 118, 11987; Y. Harabuchi, R. Yamamoto, S. Maeda, S. Takeuchi, T. Tahara, and T. Taketsugu, J. Phys. Chem. A 2016, 120, 8804; T. Tsutsumi, Y. Harabuchi, R. Yamamoto, S. Maeda, T. Taketsugu, Chem. Phys. 2018, 515, 564;
[5] H. Kuramochi, T. Tsutsumi, K. Saita, Z. Wei, M. Osawa, P. Kumar, L. Liu, S. Takeuchi, T. Taketsugu, T. Tahara, Nature Chem., 2024, 16, 22.
[6] T. Tsutsumi, Y. Ono, T. Taketsugu, Chem. Commun. 2021, 57, 11734; Topics in Current Chemistry (New Horizon in Computational Chemistry Software) 2022, 380, 19; J. Chem. Theory Comput. 2022, 18, 7483.
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