[QE-users] Difference between Geometry Optimization and a SCF calculation

[Chaman Gupta]

Hey everyone,

Might be a very naive question, but I have been very confused with this
recently.

I have a 'Si - simple hexagonal' cif file. I want to see the band structure
and/or the band gap (HOMO - LUMO).
1. I ran a 'scf' calculation on BURAI (a GUI for QE). It generated an
output file which gave me the Total energy and the energy of HOMO and LUMO.
2. Now separately, I ran a 'geometry optimization' calculation (both
'relax' and 'vc-relax': thus 2 different calculations), again on BURAI, and
I got an output file, which gives me Total energy and energy of HOMO and
LUMO.

*I specified nbnd = 8 (no. of bands) for both the above mentioned
calulations*

I am confused as in which one is correct or more reliable. And also when
should we use which calculation?

Help is really appreciated.

Regards,

*Chaman Gupta*
Graduate Research Student, *Novosselov Research Group
<http://depts.washington.edu/nrglab/>, UW*
Graduate Research Student, *Pauzauskie Research Group
<https://depts.washington.edu/pzlab/wordpress/>, UW*
University of Washington Seattle, *M.S. in Mechanical Engineering*
IIT Kharagpur, *B.Tech in Metallurgical and Materials Engineering*
*Linked In <https://www.linkedin.com/in/professorchamangupta> | Email
<chaman at uw.edu> | **P*: +1 (206) 383-3514
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