[Pw_forum] Different band gap value from the 'relax' and 'nscf'calculation.

[#TAO JUNGUANG#]

Dear Felipe
 Thanks for your help.
Yes, I knew and saw that when using relax, the initial and final
coordinates will differ. But in my case, the difference is not
significant, because the initial coordinates I used are almost
optimized. So, the that big difference (3.25eV and 1.64eV) looks
unreasonable. It confused me, and I am now wondering ,maybe, my former
run LEFT something that effect the following run. If you have time, will
you help me to test? And the input file can been seen in the attachment.
Thanks. 


Best wishes,

Tao Junguang


Dear Tao Junguang,

> order to figure out the reason, I run another one setting
> calculation='relax' with the other parameters the same, and I got the
> value of 1.64eV, which sounds quite reasonable for DFT. So I am wonder
> is any chance that the 'nscf' and 'relax' different so much ?  

Sure they  differ! calculation='relax' request an structural relaxation 
(i.e. the internal coordinates are optimized). Do your initial and final

coordinates differ significantly? In that case, the reason for the 
differences in the electronic  gaps is quite evident.

Best regards,
Felipe
-- 
Felipe Valencia Hernandez
Dipartimento di Fisica G. Galilei
Via Marzolo 8
I-35131 Padova, Italy


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