Thank you very much for the information provided. It helps me alot. From where you got this cif file. Kindly suggest me some sites from where can we get CIF files.
You could follow the dscussion below, there has details about how to perform quantum chemical computation of nonstoichometric compositions:
How do you implement non stoichiometric alloys within DFT Calculations? (http://www.researchgate.net/post/How_do_you_implement_non_stoichiometric_alloys_within_DFT_Calculations)