Is VASP capable to deal with charged slab system with NELECT?

Question on input files/tags, interpreting output, etc.

Please check whether the answer to your question is given in the VASP online manual or has been discussed in this forum previously!

Moderators: Global Moderator, Moderator

Locked
Message
Author
ziyi_wang
Newbie
Newbie
Posts: 2
Joined: Tue Mar 24, 2020 4:29 pm

Is VASP capable to deal with charged slab system with NELECT?

#1 Post by ziyi_wang » Fri Jan 08, 2021 9:43 pm

Dear researchers,

Our group is now conducting experiments on the physical absorption process of charged thin films. According to the FAQ part in the VASP wiki (https://www.vasp.at/wiki/index.php/FAQ), I know it would be hard to use VASP in the absorption of ions. However, is it possible for VASP to deal with the system with charged slabs?

In specific, we are looking at the van der Walls interaction between the methane molecule and the charged graphene layer. We set a vacuum layer around 20Å along the z-axis. According to the band structure, if the number of electrons is small, it would first fill in the orbit of the graphene. So if I change the NELECT slightly (0.05e for example), the graphene layer would be charged while the methane is still neutral. Then we calculate the van der Walls energy by subtracting the energy of charged graphene and the energy of neutral methane from the energy of the charged system energy. We can plot the energy versus distance curve without doing any relaxation.

My question is that, are these energy curves reliable? As I find out that when the distance between methane and graphene is far away, where the van der Walls interaction should be tiny, there is still a non-neglectable van der Walls energy difference between the systems with different charges. As shown in the attached figure.

Image

One of my INCAR files is shown below:

IVDW=20
LVDW_EWALD =.TRUE.

NSW=0
IBRION=-1

ISIF=2
PREC=Accurate
EDIFFG=1e-6
LWAVE=.F.
LCHARG=.F.
ISMEAR=-5
LORBIT=11
SIGMA=0.05
EDIFF=1e-7
ALGO=Fast
SYMPREC=1e-7

NELECT=136.0500

NPAR=16
KPAR=8

Thank you very much for any possible help!

Best regards,

Ziyi

martin.schlipf
Global Moderator
Global Moderator
Posts: 455
Joined: Fri Nov 08, 2019 7:18 am

Re: Is VASP capable to deal with charged slab system with NELECT?

#2 Post by martin.schlipf » Mon Jan 11, 2021 7:47 am

In general there is an issue because of the periodic replica of the added charge. This is something VASP does not intrinsically cancel automatically, so you need to find a way to address this. What you can easily try is changing the vacuum size, if your workflow is reliably canceling out this spurious interaction, you should not see a dependence on vacuum size.

I would also like to point out the work of Mauricio Chagas da Silva et al. They have collaborated with us on that project to get this feature as an external add-on compatible the upcoming release of VASP 6.2. It seems that their correction is relevant to what you want to do.

bo_peng
Newbie
Newbie
Posts: 11
Joined: Thu Sep 10, 2020 12:03 pm

Re: Is VASP capable to deal with charged slab system with NELECT?

#3 Post by bo_peng » Thu Jan 28, 2021 11:49 pm

Hi Martin,

Thank you for the clarification! Are there any tutorials/examples in the newly released VASP.6.2.0 for the charged slab corrections?

Best regards,
Bo
Bo Peng
Nevile Research Fellow, Magdalene College
Theory of Condensed Matter Group, Cavendish Laboratory
University of Cambridge

https://www.tcm.phy.cam.ac.uk/profiles/bp432
https://www.magd.cam.ac.uk/user/peng

martin.schlipf
Global Moderator
Global Moderator
Posts: 455
Joined: Fri Nov 08, 2019 7:18 am

Re: Is VASP capable to deal with charged slab system with NELECT?

#4 Post by martin.schlipf » Fri Jan 29, 2021 7:26 am

Unfortunately, there is no such tutorial so far. This is a very recent feature and the paper seems not even to be officially out yet. I suggest to contact the original authors of this feature, perhaps they may give you a hand.

ziyi_wang
Newbie
Newbie
Posts: 2
Joined: Tue Mar 24, 2020 4:29 pm

Re: Is VASP capable to deal with charged slab system with NELECT?

#5 Post by ziyi_wang » Wed Feb 03, 2021 10:07 pm

Thanks a lot, Martin! I am trying to use relative energy to solve this problem. I would also read the paper you posted. Thanks again.

Locked