Thanks for replying dear Andrei 
My calculation started with bulk zno( four atoms per unit cell ) .I used 
lattice parameters and atoms position of experimental data and 
bandstructure,DOS is ok. 
Then i made supercell 2*1*2 of the unit cell using wien2k and save it as 
zno.xsf . its shape using xcrysden was okey. 
Then for constructing vacuum  i increased lattice parameter in x,y,z direction 
(see the enclosed zno.xsf , super_zno.xsf file). is this procdure is wright for 
adding vacuum? 
 But surprisingly if you look at the super_zno.xsf you will see that there is a 
a gap between Zn atoms!!! with no any bonds. What dose this mean and what has 
happen? 
Even I have not done any relaxation and calculations?  

Best Regards
Mahshid


      

Attachment: ZnO.xsf
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Attachment: super_zno.xsf
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