[Pw_forum] why do we need to relax the atomic coordinates obtained from cif file

[janardhan H.L.]

Dear all,

I am an experimentalist wanted to use QE for obtaining DOS and band structure. As I was recently got introduced to QE and also most of the theory, I have a small question. I searched in PW archives and didnt find the answer looking for. My question is as follows,

While solving a crystal structure we take lots of parameter and refine the crystal structure to at most accuracy. If we take this atomic coordinates for QE scf calculation does it affect the results obtained? 

If yes why, and relaxing the atomic positions may result in different coordinates which may be different from the input file which may not give the similar XRD patterns. Hence by relaxing the atomic coordinates from cif file and using for further calculations may not match to experimental results. Please comment on this.




with respectful regards

Janardhan H L
Research Fellow
Poornaprajna Institute of Scientific Research 
Bangalore India
www.ppisr.res.in
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