Dear Chaman,
Essentially, a geometry optimisation moves the atoms around to reduce
the energy of the system. The energy of the system is calculated using
an scf calculation. The geometry optimisation is therefore a bunch of
scf calculations strung together, with a succession of atomic positions
approaching the minimum-energy positions.
You should carry out a geometry optimisation if you suspect that your
atoms are not in the ground state for your given parameters.
Best,
Michael Hutcheon
TCM group, Cambridge University
On 2020-05-20 11:37, Chaman Gupta wrote:
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 [1], UW_
Graduate Research Student, _Pauzauskie Research Group [2], UW_
University of Washington Seattle, _M.S. in Mechanical Engineering_
IIT Kharagpur, _B.Tech in Metallurgical and Materials Engineering_
Linked In [3] | Email | P: +1 (206) 383-3514
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Links:
------
[1] http://depts.washington.edu/nrglab/
[2] https://depts.washington.edu/pzlab/wordpress/
[3] https://www.linkedin.com/in/professorchamangupta
[4] http://www.max-centre.eu/quantum-espresso
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