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Dynamical behavior of one-dimensional water molecule chains in zeolites: nanosecond time-scale molecular dynamics simulations of bikitaite

Demontis, Pierfranco and Stara, Giovanna and Suffritti, Giuseppe Baldovino (2004) Dynamical behavior of one-dimensional water molecule chains in zeolites: nanosecond time-scale molecular dynamics simulations of bikitaite. The Journal of Chemical Physics, Vol. 120 (19), p. 9233-9244. eISSN 1089-7690. Article.

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DOI: 10.1063/1.1697382

Abstract

Nanosecond scale molecular dynamics simulations of the behavior of the one-dimensional water molecule chains adsorbed in the parallel nanochannels of bikitaite, a rare lithium containing zeolite, were performed at different temperatures and for the fully and partially hydrated material. New empirical potential functions have been developed for representing lithium–water interactions. The structure and the vibrational spectrum of bikitaite were in agreement both with experimental data and Car–Parrinello molecular dynamics results. Classical molecular dynamics simulations were extended to the nanosecond time scale in order to study the flip motion of water molecules around the hydrogen bonds connecting adjacent molecules in the chains, which has been observed by NMR experiments, and the dehydration mechanism at high temperature. Computed relaxation times of the flip motion follow the Arrhenius behavior found experimentally, but the activation energy of the simulated system is slightly underestimated. Based on the results of the simulations, it may be suggested that the dehydration proceeds by a defect-driven stepwise diffusion. The diffusive mechanism appears as a single-file motion: the molecules never pass one another, even at temperatures as high as about 1000 K, nor can they switch between different channels. However, the mean square displacement (MSD) of the molecules, computed with respect to the center of mass of the simulated system, shows an irregular trend from which the single-file diffusion cannot be clearly evidenced. If the MSDs are evaluated with respect to the center of mass of the molecules hosted in each channel, the expected dependence on the square root of time finally appears.

Item Type:Article
ID Code:330
Status:Published
Refereed:Yes
Uncontrolled Keywords:Water, molecular clusters, molecular dynamics method, atom-molecule collisions, hydrogen bonds, solvation, diffusion, potential energy surfaces, nuclear magnetic resonance, vibrational states, zeolites, nanostructured materials, chemical relaxation, lithium compounds, aluminium compounds, silicon compounds
Subjects:Area 03 - Scienze chimiche > CHIM/02 Chimica fisica
Divisions:002 Altri enti e centri di ricerca del Nord Sardegna > INSTM-Consorzio Interuniversitario Nazionale per la Scienza e la Tecnologia dei Materiali, Unità di ricerca di Sassari
001 Università di Sassari > 01 Dipartimenti > Chimica
Publisher:American Institute of Physics
eISSN:1089-7690
Publisher Policy:Depositato in conformità con la politica di copyright dell'Editore
Deposited On:18 Aug 2009 10:02

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