[QE-users] [EXT] Help with Environ

Wed Mar 6 21:00:42 CET 2019

Hi Sankha,

Great that the levels are now closer! For the output my guess is that this is (sort of) a bug, due to the fact that during an NSCF calculation the code does not pass by the corresponding output routine of Environ. The correction really only depends on the size of the cell and on the valence of the atoms in the cell, so for two calculations with the same atoms and the same cell, the number should be the same. Thus, you can safely use the same number reported in the SCF calculation also for the NSCF one. I will check in the code why it is not printed in the NSCF calculation, but if it is a bug, it will only be fixed in the next release of Environ. Thanks for reporting the problem, please let me know if you have other issues.

Best,

Oliviero

Oliviero Andreussi
--
Assistant Professor
Department of Physics
University of North Texas
Email: oliviero.andreussi at unt.edu<mailto:oliviero.andreussi at unt.edu>
Phone: +1-(940)-369-5316
Skype: olivieroandreussi
Web: https://sites.google.com/site/olivieroandreussi

On Mar 6, 2019, at 11:10 AM, Sankha Mukherjee <sankha.mukherjee at utoronto.ca<mailto:sankha.mukherjee at utoronto.ca>> wrote:

Dear Professor Andreussi,

I realized I did not include that additional flag environ_restart for the nscf runs. Thank you.

The printed Fermi levels are closer in value now, but the ‘pbc correction’ is still only output for the scf run and not the nscf run.

scf gives a Fermi level of -3.9197 eV which needs to be corrected by -0.1819 eV, and nscf gives only a Fermi level of -3.9185 eV without the correction. Please advise, which value should we use.

Best,

Sankha

From: users <users-bounces at lists.quantum-espresso.org<mailto:users-bounces at lists.quantum-espresso.org>> On Behalf Of Andreussi, Oliviero
Sent: March-05-19 10:20 PM
To: Quantum Espresso users Forum <users at lists.quantum-espresso.org<mailto:users at lists.quantum-espresso.org>>
Subject: Re: [QE-users] [EXT] Help with Environ

Hi Sankha,

I am sorry I misunderstood your previous message. The discrepancy that worries you is between nscf and scf, not between dielectric and vacuum, correct? My guess is that you are not running the nscf with Environ. You need to specify environ_restart = true in the Environ input file, and maybe you should also set environ_thr to a large value, otherwise PW will not pass through the Environ calculation. Let me know if this solves the problem or if you had already setup the calculation like this. As for the printout of the Fermi correction for the parabolic correction, I am not sure why is not in the output, it may be due to the problem above or a different issue, but it should be the same as in the scf calculation.

Best,

Oliviero

On Mar 5, 2019, at 9:08 PM, Sankha Mukherjee <sankha.mukherjee at utoronto.ca<mailto:sankha.mukherjee at utoronto.ca>> wrote:
Dear Professor Andreussi,

Thank you for your detailed response.

I would just like to confirm that the correction for which you are referring is the line that states "the Fermi energy shift due to the parabolic pbc-correction is  -0.1819 ev".

For the nscf output, however, I cannot seem to find the equivalent correction line, and the Fermi energy is output without any additional lines after it.

The printed Fermi energy in the scf run file is -3.9197 eV, and with the correction becomes -4.1016 eV. However, in the nscf output the Fermi energy is printed as -1.7056 eV.

Best,

Sankha Mukherjee

University of Toronto

From: users <users-bounces at lists.quantum-espresso.org<mailto:users-bounces at lists.quantum-espresso.org>> On Behalf Of Andreussi, Oliviero
Sent: March-05-19 8:57 PM
To: Quantum Espresso users Forum <users at lists.quantum-espresso.org<mailto:users at lists.quantum-espresso.org>>
Subject: Re: [QE-users] [EXT] Help with Environ

Hi Sankha,

Thanks for reporting your doubts with Environ. Similarly to the potential, the Fermi energy is defined up to an additive constant which is not uniquely defined. If you introduce the dielectric, the Fermi energy changes. If you look at the value of the Fermi energy with respect to the value of the potential in the vacuum, I.e. the workfunction, and you compare it to the same quantity in solution (a.k.a. the potential of zero charge) you should expect them to be different. Having said this, the way the potential is shifted inside of Environ is probably different from a standard calculation in vacuum and depends on the pbc correction that you use. Please pay attention to the fact that in an Environ calculation there is a correction that needs to be added to the Fermi energy and is printed out in the output a few lines after the Fermi energy itself.

I hope this helps, if you have other problems or doubts, please let me know.

Regards,

Oliviero Andreussi
University of North Texas

On Mar 5, 2019, at 7:39 PM, Sankha Mukherjee <sankha.mukherjee at utoronto.ca<mailto:sankha.mukherjee at utoronto.ca>> wrote:
Hello all,

I am working on catalysis related projects using Environ. When running SCF and subsequently NSCF using Environ I have noticed a discrepancy between the values of the Fermi levels when introducing a dielectric constant >1. Considering the vacuum case, these Fermi energies are nearly identical however.

I was wondering how the permittivity of the medium could be causing this contrast, and if there is one of these values I can trust more than the other.

Thanks,

Sankha Mukherjee
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