Molecular Dynamics Studies of Two Particles in a Rectangular Box: Hard-Sphere and Square-Well Interactions
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Molecular Dynamics Studies of Two Particles in a Rectangular Box: Hard-Sphere and Square-Well Interactions SOONG-HYUCK SUH∗ Department of Chemical Engineering, Keimyung University, Taegu 704-701, Korea [email protected]
JAE-WOOK LEE Department of Chemical Engineering, Seonam University, Namwon 590-711, Korea HEE MOON Faculty of Applied Chemistry, Chonnam National University, Kwangju 500-757, Korea JAMES M.D. MACELROY Centre for Synthesis and Chemical Biology, the Conway Institute of Biomolecular and Biomedical Research, Department of Chemical Engineering, University College Dublin, Belfield, Dublin 4, Ireland
Abstract. Molecular dynamics simulations have been carried out for the simple few-body systems of two particles confined within a 2-dimensional rectangular box. The two different sets of interaction potentials between the colliding particles were employed in these studies: hard-sphere and square-well interactions. Wall pressures, the wall/particle and the particle/particle collision frequencies, and the position autocorrelation functions were computed to examine the thermodynamic, structural and time-dependent properties of such systems. Detailed dynamic effects are discussed to describe configurational particle trajectories including fast/slow relaxation processes observed in the position autocorrelation functions. Keywords: molecular dynamics simulation, finite few-body system, hard-sphere, square-well
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Introduction
Whether it is solid-like or fluid-like, the behavior of particles, or molecules, confined within a given structural system is often of significant importance in science and engineering applications, e.g., nanoporous and microporous materials such as carbon nanotubes, zeolites, and porous metal oxide compounds for heterogeneous catalysts and separation processes. From a simple structural point of view, the behavior will be solid-like if the particle center-of-mass positions are restricted to sub-nanometer spatial fluctuations and they cannot ex∗ To
whom correspondence should be addressed.
change their positions with neighboring particles. In a fluid-like phase, particles are subject to less stringent confinement and may move freely, exchanging their positions with each other. In the usual many-body systems, the statistical mechanical definition is related to the so-called thermodynamic limit, where the system volume and the number of particles tend to infinity while the number density is kept to be fixed in the thermodynamic sense. In recent years, it has been gathered considerable attention to study the finite few-body systems, and more rigorous treatments are possible by means of analytical considerations and computer simulations (Nemeth and Lowen, 1998; Gonzalez et al., 1998; Roman et al.,
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Suh et al.
1999, 2003; Cao et al., 2004). There have been observed quite different effects in the finite few-body systems, which are not emerged in the infinite bulk behavior. For instances, in the system of the finite hard disks in a circular cavity, Nemeth and Lowen (1998) have reported the tra
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