Cubic structure electroneutrality

Models of Ni-Fe sulfide were constructed as cut offs from the crystal structure of violarite [110] with space group Fd-3m and cubical unit cell with the parameters a = b = c = 9.465 A. Due to total structural changes caused by the optimization the original model was modified, its size was decreased by removal of the ambiguous part. The new model consists of one Fe, one Ni atom, and six sulfur atoms. Dangling bonds that occur on four sulfur atoms were saturated by the hydrogen atoms to ensure the electroneutrality of the entire system. 

Wustite is a nonstoichiometric microheterogeneous solid. Its idealized structure is rather similar to the magnetite structure. Both lattices are built from a cubic, close packed, oxygen lattice with the iron ions located only in octahedral voids for wustite, and in both octahedral and tetrahedral voids for magnetite. Wustite is thermodynamically metastable below 833 K but can be easily supercooled to room temperature. The composition of the material is variable and always deficient in iron Fei j,0 with x varying from 4.5% to 11%. Electroneutrality is preserved by the presence of Fe ions. These ions and the holes in the iron sublattice are not statistically distributed throughout the material but form a variety of clusters centered around the ferric ions placed in tetrahedral interstitial sites. ... 

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