Modelling the sodalite mineral

Furthermore, the strength of this bond in valence units (v.u) is 1/4, because the monovalent anion has four ions coordinated to it. Brown and Shannon [66] developed an empirical procedure for relating the bond strength in terms of v.u to bond length, i.e. 

Using Pythagoras s theorem, the relationship between fractional coordinates for oxygen atom (x,y,z) and cation at X, X, Xc can be derived  

For predicting the cell parameter, Ho, for a particular sodalite an iterative computer program was developed incorporating all the above equations. It starts with an,j =7.75A 

Note the tetrahedral disposition of Cation C around the Anion A and the coordination of C to the nearest set of oxygen atoms O in the 6-ring. (Adapted from B. Beagley and J.O. Titiloye [65]) 

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