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[Sharat Chandra <sharat_c@yahoo.com>]

you might be interested in the following reference:

Soft modes and NTE in Zn(CN)2 from Raman spectroscopy and first
principles calculations.
Authors: T. R. Ravindran, A. K. Arora, Sharat Chandra, M. C.
Valsakumar, N. V. Chandra Shekar
http://in.arxiv.org/abs/0704.0161v1

The disordered phase of the zn(cn)2 requires that the 8e site is
occupied by the C and N atoms with 50% probability. This can be easily
simulated in the diffraction data analysis by virtual atom
approximation, but is quite difficult to do in dft calculations. So, we
have to imagine a series of structures with two of the positions of the
Zn-(CN) tetrahedra occupied by C atoms and the other two by N atoms. If
we carry out this exercise, we find that there are only three possible
combinations taking the C-N bond into account, as it is this bond which
defines the character of the compound. Hope this helps.

regards
sharat


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