[Wien] Regarding the electronic properties of band gap of super cell

[Peter Blaha]

The results will of course depend on the way you arranged the 2 
impurities in the 2x2x2 cell.

Did you arrange them in the same way as they would be arranged in a 
doubled 1x2x2 supercell ??? (use supercell 2x1x1 starting from 1x2x2 and 
compare the resulting arrangement of your impurities).

This is the common mistake related to i) small supercells or ii) larger 
concentrations:

You are not simulating a disordered alloy with 6.5% impurities, but an 
ordered "compound" with a specific structure (which is never observable 
in experiment.

One needs to use larger supercells and either a "quasi-random structure" 
or at least test a couple of arrangments of your impurities (more 
nearest-neigbors or far away, ...)



On 3/11/20 11:46 AM, Indranil mal wrote:
> Hello everyone We are trying to calculate electronic properties of super 
> cell structures for a specific doping percentages. Where the unit cell 
> is from zinc blend space group with four atoms each anion and cation 
> total 8 atoms for and a doping concentration of 6.25%.  We have tried 
> with two different supper cell
> 
> 1. Incorporated 2 impurity atom in p type 2x2x2 supper cell consist of 
> 32 atoms each anion and cation and total 64 atoms. [(2*100/32)=6.25]
> 
> 2. Incorporated 1 impurity atom in p type 1x2x2 supper cell consist of 
> 16 atoms each anion and cation and total 32 atoms. [(1*100/16)=6.25]
> 
> For both the cases we have considered the same ec cc fc for convergence 
> and  same XC and mBJ potential and same numbers of k points. The 
> structural properties are more or less same for both the case.
> 
> However, the the electronic properties are not same for the cases. It 
> will be helpful if you kindly suggest us for corrections to get same 
> result.
> 
> We have constrain in computation resources and that is why we want to 
> compute greater impurity percentage with smaller supper cell structures.
> 
> 
> Thanking you
> Indranil
> 
> 
> 
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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