[Wien] Control of very small fraction of atoms in alloy

[Seongjae Cho]

Dear users, 
As an electronic device researcher, I started to run Wien2k recently. What I'm interested in is to see what really happens to the electronic structures (bandgap and extraction of carrier mobility from it, etc.) in an alloy when the fraction of one of the comprising atoms is very slightly changed, by like 1 % or below step. Maybe we can think about Si1-xGex for x = 0.015, 0.02, 0.025, etc, as an example. 
If I make an approach through the supper-lattice method, i.e., if I first replace one of the A atoms by a B atom and send the unit cell to many directions, it would give a very large portion itself and very large portion spacing as well. Replacement of even only 1 or 2 atoms out of 8 atoms in the diamond structure, for example, would make 12.5% and 25% atomic fraction and fraction changes. So, a simple idea that struck me was it would be really good if there might be a way to put extrinsic atoms one by one into that already made supper cell having 100 or so basis atoms. 
I'm wondering if this sounds good and if it is a feasible method that has been accepted in running Wien2k. But, it's an idea yet even though it is a right way. So, it will be greatly appreciated if you share some know-hows to make this happen. 
Thank you for your kind helps and communications in advance. 
- Sincerely, Seongjae. 
I'm a novice in this area but having a real fun with this. Thanks for the supporing group and all the other users. 
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