[Pw_forum] Relaxation of impurity in bulk materials

[Izaak Williamson]

Hello everyone,

I am trying to study impurities in SiC bulk material. For this, I use a big 
unitcell of 2x2x2. I do not understand how to do a relaxation in this system, 
ie, which atoms should be kept fixed? I was thinking that the unitcell boundary 
atoms would automatically be kept fixed but that does not seem to be the case. 
Any help will be much appreciated.
 
-- 
Izaak Williamson
Research Assistant
Physics Department
Boise State University
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