[Pw_forum] selection of number of unit cells

[chaitanya varma]

I am presently working on Ni-Zn ferrite doped with divalent and trivalent ionsi did work by synthesizing samples using sol-gel methods and did other experimental work.now i am interested in giving explanation by doing DFT work.
in this regard i want to how can two or more unit cells be selected (given) to do calculation
one unit contains 56 atoms [8*  (NiZn)Fe2O4- molecules- spinel phase]if i doped like 0.04 Co2+ in place of Ni2+i may need more unit cells to know the effect of Cobalt. since even small amount of cobalt is enough to change magnetic anisotropy drastically. Chaitanya Varma M  
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