[Wien] How to choose the substitution site when performing the calculation of doping?

[Stefaan Cottenier]

>    Thank you very much for your valuable and informative advice. 
> Taking the 2*2*2 supercell of TiC as the example, would you like to 
> give me some advice on how to substitute the original atoms of 
> supercell according to the two different instances:(1)impurities that 
> are closely packed into clusters, (2)impurities that are as 
> homogeneously disitributed over the supercell as possible?

Do various substitutions and visualize the cells by Xcrysden: you will 
*see* how the distribution of your impurities is.

>    Besides, how about the substitution of original atoms when there 
> are more than one type original atom (for example the Si atom in 
> FeSi2) in the supercell?

It all depends on the physics of your problem. Some impurities might 
'like' one of the sites over the other, other impurities don't. 
Calculate the total energies and compare ?

Stefaan


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