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We apply a Monte Carlo technique specialized for the simulation of rare events to study the activated counterions motions in the aluminosilicate Na[sup +]-mordenite. Mean activation barriers are obtained from minimum energy paths calculated on realistic potential energy surfaces by using a Metropolis algorithm. Energy barriers for Na[sup +] hops calculated for lattices with various Si/Al ratio are found in good agreement with the Na[sup +] detrapping energies measured by thermally stimulated current spectroscopy. One shows that the dielectric activated motions of Na[sup +] proceed between degenerated many-body ground states with different dipolar moment by either sequential or collective hopping motions. This provides a first microscopic description of dielectric relaxation measured in zeolites. [ABSTRACT FROM AUTHOR]

The evolution of the activation energy of the conductivity depends on the nature of the exchanged cations, and differs in faujasites X and Y. This surprising phenomenon, reported in many works, is not yet satisfactorily explained. A qualitative explanation is proposed based on well-known results obtained in the study of the interactions between chemical species, by means of density functional theory. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]