[QE-users] [EXT] Question about parabolic correction method in Environ

[Andreussi, Oliviero]

Hi Bingxin,

The pbc_correction = parabolic option in Environ is not necessary, you should be able to perform the implicit solvent calculation even with pbc. However, it is highly recommended that you remove pbc artifacts if you are studying slabs systems, in particular if they have a finite dipole moment in the direction perpendicular to the slab.

Having said this, there are a couple of statements in your email that I find confusing. Is your system neutral or charged? When you say that the parabolic correction cannot do the dipole correction for the neutral slab, you mean a slab without a dipole or a slab without a charge?

If you are studying charge neutral slabs, then you should be able to apply the parabolic correction to both the slab without the hydroxyl and the slab with the hydroxyl, both in vacuum and in solution. All these simulations should work reasonably smoothly in Environ. Note that if you want to only perform the parabolic correction on a slab without the implicit solvent, in environ you need to specify env_electrostatic = .true.. Otherwise, if there is no dielectric and no diffuse layer, Environ will skip the electrostatic corrections.

If you are studying a charged slab, i.e. you are adding negative hydroxyls to your slab, the parabolic correction alone will not be a physically sound model. Charged periodic 2D systems have infinite energy, in reality the charge on the slab should be compensated by the electrolyte in solution. Thus, even though the parabolic correction will work, the energy you will get will depend on the size of the cell (growing linearly as you increase the direction perpendicular to the slab). For a realistic model you would need to include a diffuse layer, which can still be done with Environ. The easiest option is to use pbc_correction = ‘gcs’, but you would need to specify a couple of other details. If this is what you are trying to do, let me know and I will try to help.

Hope this helps.

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 Feb 26, 2020, at 10:46 AM, Li, Bingxin <bingxin.li18 at imperial.ac.uk<mailto:bingxin.li18 at imperial.ac.uk>> wrote:

Dear all,

Recently I am using Environ + QE to calculate the work function of Mg(0001) surface based on slab model. I have calculate the work function of slab model  in vacuum. Now I want to calculate that in water (implicit solvent). But I have add some hydroxyl groups on the surface, which means it is necessary to do the dipole correction to obtain accurate vacuum potential. There is a parabolic correction method in Environ, which can treat the charged slab in vacuum/solvent. However, I find this method cannot do the dipole correction for the neutral slab. Can I closed PBC  term in the environment input file and do the dipole correction in the QE input? Is this parameter (Pbc: parabolic) necessary to do the implicit solvent calculation?

Could anyone understand this and help me?

Best Regards,
Bingxin
_______________________________________________
Quantum ESPRESSO is supported by MaX (https://nam04.safelinks.protection.outlook.com/?url=www.max-centre.eu%2Fquantum-espresso&data=02%7C01%7Coliviero.andreussi%40unt.edu%7C818a0dd2d5e14e76402308d7badb90c9%7C70de199207c6480fa318a1afcba03983%7C0%7C0%7C637183324514973413&sdata=J%2FsTe9Z17AhMuTOoABA4E2G1GrxWsAlkxqC6ZryDhmg%3D&reserved=0)
users mailing list users at lists.quantum-espresso.org<mailto:users at lists.quantum-espresso.org>
https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.quantum-espresso.org%2Fmailman%2Flistinfo%2Fusers&data=02%7C01%7Coliviero.andreussi%40unt.edu%7C818a0dd2d5e14e76402308d7badb90c9%7C70de199207c6480fa318a1afcba03983%7C0%7C0%7C637183324514973413&sdata=2jLvz7iSQer99DABHq2obWb%2FgWVbOvVp7n0ECfKwCI4%3D&reserved=0

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20200226/1bd34770/attachment.html>