External mode formalism Is applied t o study phonons In Cali04. The e f f e c t i v e I o n i c charges of t h e Coulomb I n t e r a c t i o n s and t h e e f f e c t i v e I o n i c r a d i i of Born-Mayer shortrange p o t e n t i a l a r e determined s o t h a t t h e dynamical equilibrium conditions a r e s a t i s f i e d and l a t t i c e energy is of r i g h t o r d e r I n comparison with o t h e r complex i o n i c c r y s t a l s . h e c a l c u l a t e d phonon diapers i o n r e l a t

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... i o n s along[OOa a n d C 1 l~d i r e c t l o n s a r e I n reasonable agreement with t h e neutron data. The generalised LST r e l a t i o n s computedwith our model agree with t h e IR data. Zone c e n t r e phonons In few o t h e r s c h e e l i t e s are a l s o