[QE-users] Last SCF step of a vc-relax job in DFT+U

[Mahmoud Payami Shabestari]

Hi Iurii,

Thank you for comments.

What I understood, is that it helps to distinguish at least two cases:



1- If the energy of the final scf is more or less the same with that of 
vc-relax, but the final pressure is large, then the cure is just to increase 
ecut.

2- If the energy of the final scf differs significantly, then it was 
converged to other state. In this case, the cure is to start a separate scf 
with new cell parameters and atomic positions.

Moreover, I feel that using a relatively large mixing_beta may cause 
oscillation between metastable states and lead to no scf convergence.



Bests,

Mahmoud











From: Iurii TIMROV via users <users at lists.quantum-espresso.org>
To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
Date: Thu, 1 Dec 2022 08:05:28 +0000
Subject: Re: [QE-users] Last SCF step of a vc-relax job in DFT+U



> What are the advantages of this choice?




Without this "trick", for some systems the final SCF calculation might not 
converge to the same ground state as in the vc-relax run.




Iurii




--
Dr. Iurii TIMROV
Senior Research Scientist
Theory and Simulation of Materials (THEOS)
Swiss Federal Institute of Technology Lausanne (EPFL)
CH-1015 Lausanne, Switzerland
+41 21 69 34 881
http://people.epfl.ch/265334
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Mahmoud 
Payami Shabestari <mpayami at aeoi.org.ir>
Sent: Wednesday, November 30, 2022 9:19:52 PM
To: Quantum ESPRESSO users Forum
Subject: Re: [QE-users] Last SCF step of a vc-relax job in DFT+U


I found the following statement in release-notes:


New in 6.7 version:
  * In vc-relax with Hubbard corrections, the final SCF calculation is done 
by
    reading atomic occupations from file produced during the vc-relax
    (rather than recomputing them from scratch).


What are the advantages of this choice? Does it inform about possible 
transition among metastable states?


Mahmoud
From: "Mahmoud Payami Shabestari" <mpayami at aeoi.org.ir>
To: "users at lists.quantum-espresso.org" <users at lists.quantum-espresso.org>
Date: Wed, 30 Nov 2022 10:49:09 +0330
Subject: [QE-users] Last SCF step of a vc-relax job in DFT+U


Dear All,
Hi.


As far as I know from, in a vc-relax job for a normal system, when the 
calculated pressure in the last scf (which starts with optimized lattice 
parameters and atomic positions, while keeping other input values fixed) is 
much higher than default 0.5kbar value, it implies that one has to increase 
ecutwfc, ecutrho, ... until this large difference disappears.
In a DFT+U run, I encountered such a problem. But when I performed a 
separate scf but with optimized cell parameters and atomic positions, I get 
the optimized value for pressure say 0.01 kbar, which is perfect. I am using 
QE-7.1.
Does it mean that in the last scf run of vc-relax the diagonalised 
ocuupation matrices are used instead of the values specified in the input?
Thanks in advance.


Best regards,
Mahmoud Payami
NSTRI, AEOI, Tehran, Iran


Email: mpayami at aeoi.org.ir
Phone: +98 (0)21 82066504
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