[QE-users] (no subject)

[Baer, Bradly]

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 <users-bounces at lists.quantum-espresso.org> on behalf of Malathe Khalil <malathe.zero1 at gmail.com>
Sent: Sunday, May 17, 2020 11:43 AM
To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
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, <fabrizio.cossu at apctp.org<mailto:fabrizio.cossu at apctp.org>> wrote:


On Sun, 17 May 2020 at 22:19, Malathe Khalil <malathe.zero1 at gmail.com<mailto:malathe.zero1 at gmail.com>> 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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