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Gyration-radius dynamics in structural transitions of atomic clusters

Yanao, Tomohiro and Koon, Wang S. and Marsden, Jerrold E. and Kevrekidis, Ioannis G. (2007) Gyration-radius dynamics in structural transitions of atomic clusters. Journal of Chemical Physics, 126 (12). Art. No. 124102. ISSN 0021-9606. http://resolver.caltech.edu/CaltechAUTHORS:YANjcp07

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Abstract

This paper is concerned with the structural transition dynamics of the six-atom Morse cluster with zero total angular momentum, which serves as an illustrative example of the general reaction dynamics of isolated polyatomic molecules. It develops a methodology that highlights the interplay between the effects of the potential energy topography and those of the intrinsic geometry of the molecular internal space. The method focuses on the dynamics of three coarse variables, the molecular gyration radii. By using the framework of geometric mechanics and hyperspherical coordinates, the internal motions of a molecule are described in terms of these three gyration radii and hyperangular modes. The gyration radii serve as slow collective variables, while the remaining hyperangular modes serve as rapidly oscillating “bath” modes. Internal equations of motion reveal that the gyration radii are subject to two different kinds of forces: One is the ordinary force that originates from the potential energy function of the system, while the other is an internal centrifugal force. The latter originates from the dynamical coupling of the gyration radii with the hyperangular modes. The effects of these two forces often counteract each other: The potential force generally works to keep the internal mass distribution of the system compact and symmetric, while the internal centrifugal force works to inflate and elongate it. Averaged fields of these two forces are calculated numerically along a reaction path for the structural transition of the molecule in the three-dimensional space of gyration radii. By integrating the sum of these two force fields along the reaction path, an effective energy curve is deduced, which quantifies the gross work necessary for the system to change its mass distribution along the reaction path. This effective energy curve elucidates the energy-dependent switching of the structural preference between symmetric and asymmetric conformations. The present methodology should be of wide use for the systematic reduction of dimensionality as well as for the identification of kinematic barriers associated with the rearrangement of mass distribution in a variety of molecular reaction dynamics in vacuum.


Item Type:Article
Additional Information:©2007 American Institute of Physics. (Received 23 June 2006; accepted 25 January 2007; published online 22 March 2007) The authors thank Aron Kuppermann and Kazuo Takatsuka for valuable discussions. This work was partially supported by NSF-ITR Grant No. ACI-0204932, ICB-ARO Grant No. DAAD19-03-D-0004, and NSF-DMS-0505711. One of the authors (T.Y.) has also been supported by JSPS Research Fellowships for Young Scientists. Another author (I.G.K.) gratefully acknowledges the support of a Guggenheim Fellowship.
Subject Keywords:atomic clusters; molecular configurations; potential energy surfaces; potential energy functions; isomerisation; reaction kinetics theory
Record Number:CaltechAUTHORS:YANjcp07
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:YANjcp07
Alternative URL:http://dx.doi.org/10.1063/1.2710272
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7696
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:22 Mar 2007
Last Modified:26 Dec 2012 09:34

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