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Unformatted text preview: I The twobody term consists of three term as follows: U 2 = H ij r ij + Z i Z j r 1 2 ( i Z 2 j + j Z 2 i ) r 4 exp [ r / r 4 s ] (4) I The terms are: (1) Steric repulsion due to ionic sizes (2) Coulomb interactions to take into account charge transfer (3) Chargedipole interaction due to electronic polarizabilities I Above, H ij and ij are the strengths and exponents of the steric repulsion, Z i and i represent the effective charge and electronic polarizability of the i th ion, respectively I For A 4 + and X 2 the effective charges are + 4 Q and 2 Q , respectively, where Q is the unit of charge transfer I The exponential screening term in the chargedipole interaction provides a reasonable cutoff for the r 4 interaction I The value of the decay length r 4 s is taken to be a few so that the magnitude of the chargedipole potential is reduced to a few percent of the term without the exponential I Although there are six threebody terms in the interaction potential or AX 2type systems, the two most important terms involve...
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This note was uploaded on 02/14/2012 for the course CSE 6590 taught by Professor Kotakoski during the Winter '12 term at York University.
 Winter '12
 Kotakoski

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