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

[M.J. Hutcheon]

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 
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso [4])
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users

 

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20200520/dceed5e6/attachment.html>