Phonon-orientational coupling in sodium nitrite |
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Authors: | R M Lynden-Bell M L Klein I R McDonald |
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Institution: | (1) Department of Theoretical Chemistry, University Chemical Laboratory, Lensfield Road, CB2 1EW Cambridge, England;(2) Chemistry Division, National Research Council of Canada, K1A 0R6 Ottawa, Canada;(3) Department of Physical Chemistry, Lensfield Road, CB2 1EP Cambridge, England |
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Abstract: | Molecular dynamics calculations on a model of NaNO2 in its orientationally disordered paraelectric phase are used to examine the coupling between translational phonon displacements and the anion orientations. The simulations are analyzed using the theory of Michel and coworkers. The extent of phonon-orientational coupling is measured by a wave vector dependent parameter
2, whose behaviour is found to be influenced by changes in temperature. We show that
2=1 is equivalent to the Heine-McConnell condition for the formation of an incommensurate phase. While the interionic potential that we employ leads to a disordered crystal exhibiting many of the properties of NaNO2, inadequacies of the model are clearly evident. |
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