The dynamics of an isolated polymer chain has irreversible aspects that lead to the decorrelation of configurational properties over time. For simple mechanical models with time reversible equations of motion, the irreversibility is a consequence of the chaotic nature of the dynamics which, for a many body system, is expected to result in ergodic mixing. Here we study a fixed bond length N-mer interaction-site chain with fixed total energy and angular momentum. For N>or=4 the equations of motion for such a chain are nonintegrable and chaotic dynamics is expected. We directly assess the ergodicity of short repulsive Lennard-Jones chains by comparing phase space and time averages for structural and energetic properties. The phase space averages are determined from the exact microcanonical partition function while the time averages are obtained from molecular dynamics (MD) simulations. For N=4 and 5 we find that our exact phase space averages agree with the MD time averages, as expected for an ergodic system. The N=3 system is integrable and thus displays regular dynamics for which time averages are found to depend on initial conditions. In all cases, the total angular momentum is found to have a large effect on both the average chain conformation and the partitioning of the total energy between potential, vibrational, and rotational contributions. Compared to a nonrotating chain, a small to moderate angular momentum slightly speeds up the internal chain dynamics, while a large angular momentum dramatically slows the internal dynamics.
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http://dx.doi.org/10.1103/PhysRevE.78.051805 | DOI Listing |
J Chem Phys
January 2025
Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.
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Department of Optics and Optical Engineering, University of Science and Technology of China, Hefei, China.
The spin angular momentum (SAM) plays a significant role in light-matter interactions. It is well known that light carrying SAM can exert optical torques on micro-objects and drive rotations, but 3D rotation around an arbitrary axis remains challenging. Here, we demonstrate full control of the 3D optical torque acting on a trapped microparticle by tailoring the vectorial SAM transfer.
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January 2025
Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 China. Electronic address:
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Research Center of Applied Electromagnetics, Nanjing University of Information Science and Technology, Nanjing 210044, China.
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January 2025
Center for Nano Science and Technology, Fondazione Istituto Italiano di Tecnologia, Milano, Italy.
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