The angular force models of De Launay and Clark, Gazis, and Wallis are analysed by resolving the atomic displacements along three mutually perpendicular directions. It is shown that the CGW model which neglects a two-body force component perpendicular to the plane of the triangle is not equivalent t o the DAF model which neglects the three-body forces confined to the plane, for :my crystal structure and all the earlier claims regarding their equivalence are therefore spurious. The equivalence between the angular force constants of these models, the relations between these and other force constant models as well as the role played by the axially symmetric forces, in the case of b.c.c. and f.c.c. structures are discussed.
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