i want to run DFT for this structure. but whatever i try, i am unable to optimise this structure.
another problem i face is that CZTS has the chemical formula Cu2ZnSnS4. which means a single monomer will have 4 sulfur in it. but for the kesterite structure there is only one sulfur which is bonded 2Cu, 1Zn, and 1Sn.
The answer might be that monomer doesn't exist at all. Simple example - alumina formula is Al2O3, while there is no such molecules in gas phase. Either AlO or Al2O.
Are you using any symmetry and which one? CZTS is only ordered in space group I-4. The figure you are showing has Cu and Zn occupations disordered within the Cu-Zn-layers. This would be the structure of fully disordered Kesterite in space group I-42m.
If you want to express the structure in terms of monomers, you either have to use a tetrahedra with sulphur at the center, or three different ones with Cu, Zn, Sn at the centers.
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