Malathe,
I usually use vc-relax, so I dont know if it is the same in the relaxation
calculation you are using, but the last step of vc-relax is a scf calculation
with the relaxed structure. I just checked an old output file and you can
check for this line in your relax output:
End of BFGS Geometry Optimization
Final enthalpy = -395.6714252266 Ry
[...]
A final scf calculation at the relaxed structure.
The G-vectors are recalculated for the final unit cell
Results may differ from those at the preceding step.
[...]
! total energy = -395.66904355 Ry
The energies are slightly different. If you are not satisfied with this energy
you could of course perform a scf calculation on the relaxed structure and
check that the energy is the same.
Good luck,
Brad
--------------------------------------------------------
Bradly Baer
Graduate Research Assistant, Walker Lab
Interdisciplinary Materials Science
Vanderbilt University
________________________________
From: users <[email protected]> on behalf of Malathe
Khalil <[email protected]>
Sent: Sunday, May 17, 2020 11:43 AM
To: Quantum ESPRESSO users Forum <[email protected]>
Subject: Re: [QE-users] (no subject)
Dear Fabrizio
I want to calculate the adsorption energy of a molecule on a surface.
So I need the total energy of the clean slab.
Can I just take the total energy from relax calculations output or I have to
run scf ?
Thanks
Malathe
On Sun, 17 May 2020, 6:04 pm Fabrizio Cossu,
<[email protected]<mailto:[email protected]>> wrote:
On Sun, 17 May 2020 at 22:19, Malathe Khalil
<[email protected]<mailto:[email protected]>> wrote:
Dear QE users
What is the difference between the total energy generated by relax calculations
and scf calculations?
A structural relaxation is a scf calculation. Perhaps you mean a fixed point
scf calculation, i.e. without updating the positions.
When I do relax calculations do I need to do scf calculations also?
It depends on what you want to do. Do you want to compute some quantity
self-consistently? AFAIK, some calculations require a different parameter set
WRT the relaxation.
Thanks
Malathe
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