[Wien] calculation with lmbj potential
Laurence Marks
laurence.marks at gmail.com
Mon Jul 24 12:14:13 CEST 2023
You should look at the BVS, i.e. "grep Bond *tnn" and compare it to what
you have for bulk. You will see that you surface has bad values, so will be
unstable. You need to do a lot more thinking and analysis (weeks) to find a
chemically reasonable surface.
---
Professor Laurence Marks (Laurie)
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
"Research is to see what everybody else has seen, and to think what nobody
else has thought" Albert Szent-Györgyi
On Mon, Jul 24, 2023, 05:28 Peter Blaha <peter.blaha at tuwien.ac.at> wrote:
> Yes, R cells are first converted into H (making it already 3 times
> larger than the primitive R cell).
>
> The "accepting repeat atoms at z=0" makes the non-stoichiometry. It
> leads to 2 identical surfaces and inversion symmetry (cheaper calc), but
> non-stoiciometry.
> It is not always clear what the best model for a surface is. Yours is Te
> terminated, but maybe another termination is more favorable (Bi, or
> maybe another Te-layer ?)
>
> Am 24.07.2023 um 10:51 schrieb Burhan Ahmed:
> > The 6ql slab is created with 1x1x2 supercell with vacuum in Z direction
> > and accepting repeat atoms at z=0 (using x supercell program). At first
> > the x supercell convert rhombohedral cell into hexagonal and then from
> > hexagonal cell I have created the 1x1x2 supercell and then I took the
> > structure suggested by sgroup.
> >
> > Yes sorry for that I have used MSR1a method for the relaxation.
> >
> > The force convergence is set to 1 Ry.
> >
> > On Mon, 24 Jul, 2023, 2:06 pm Peter Blaha, <peter.blaha at tuwien.ac.at
> > <mailto:peter.blaha at tuwien.ac.at>> wrote:
> >
> > I'm not sure how you get a non-stoichimetric cell with a
> multiplicative
> > number of unit cells, unless you said you want to repeat the atom at
> > z=0.
> > Of course, without this extra layer, you may not have inversion and
> get
> > 2 different surface terminations in one calculation. This is the
> usual
> > problem of slabs.
> > Also symmetry will be reduced and "multiplicity" errors occur. But
> > both,
> > nn and sgroup create new struct files where this has been corrected.
> >
> > If possible, I would also go to a smaller number of layers.
> >
> >
> > Am 24.07.2023 um 10:13 schrieb Burhan Ahmed:
> > > That is very true. I made the slab using the tutorial available
> > in the
> > > wien2k user manual by executing x-supercell program. What I found
> is
> > > that the 6ql supercell consist of an extra Te atom. But whenever
> > I try
> > > to remove this atom I got multiplicity error. Sir, what is best
> > possible
> > > way of making slab with vacuum or surfaces??
> > >
> > > Thanks
> > >
> > > Regards
> > >
> > > Burhan Ahmed
> > >
> > > *Research Scholar, AUS *
> > >
> > > *From: *Laurence Marks <mailto:laurence.marks at gmail.com
> > <mailto:laurence.marks at gmail.com>>
> > > *Sent: *Saturday, July 22, 2023 6:30 PM
> > > *To: *A Mailing list for WIEN2k users
> > > <mailto:wien at zeus.theochem.tuwien.ac.at
> > <mailto:wien at zeus.theochem.tuwien.ac.at>>
> > > *Subject: *Re: [Wien] calculation with lmbj potential
> > >
> > > Others will probably give you suggestions about converging mBJ.
> Some
> > > deeper comments.
> > >
> > > The most common reason that calculations behave badly is user
> error.
> > > Sometimes this is doing the initialization wrong, often it is
> > creating
> > > an inappropriate model. Just because one can use x supercell or
> > related
> > > codes to create atomic positions does /not/ make them sensible.
> > >
> > > Your slab has a composition Bi12 Te19, i.e. it is Te rich. You
> > therefore
> > > have a reduced, n-type semiconductor with a small gap (about
> 0.1eV)
> > > which will behave badly. If you look at your BVS you will see
> > that atom
> > > Te7 is severely underco-ordinated (unstable).
> > >
> > > I doubt that your slab will ever converge to anything which
> > should be
> > > published. Surfaces are not simple, it is unfortunately too easy
> > to set
> > > something up and get it wrong. (There are many papers in the
> > literature
> > > of dubious merit.)
> > >
> > > On Fri, Jul 21, 2023 at 10:47 PM Burhan Ahmed
> > <burhan.ahmed at aus.ac.in <mailto:burhan.ahmed at aus.ac.in>
> > > <mailto:burhan.ahmed at aus.ac.in <mailto:burhan.ahmed at aus.ac.in>>>
> > wrote:
> > >
> > > Dear experts, I am doing an scf calculation taking lmbj
> > potential.
> > > My system is a slab of 6ql with a vacuum of 40 ang along
> c-axix.
> > > Whenever I try to run the scf calculation including SOC,
> > after 999
> > > iteration the scf is still not converged. I have analyzed the
> scf
> > > file, it shows the fluctuating nature. At first the selected
> > Rmt was
> > > 2.5 then I reduces it to 2.34 and again convergence failed
> > after 999
> > > cycle. I have included -hdlo and -lvns 8 switch in init_lapw
> > as it
> > > shows heavy atom. I am attaching the case.struct file. Hoping
> for
> > > any suggestion/solution.
> > >
> > > Regards
> > >
> > > Burhan Ahmed
> > >
> > > *Research Scholar, AUS *
> > >
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> > >
> > > --
> > >
> > > Professor Laurence Marks (Laurie)
> > > Department of Materials Science and Engineering
> > > Northwestern University
> > > www.numis.northwestern.edu <http://www.numis.northwestern.edu>
> > <http://www.numis.northwestern.edu <
> http://www.numis.northwestern.edu>>
> > > "Research is to see what everybody else has seen, and to think
> what
> > > nobody else has thought", Albert Szent-Györgyi
> > >
> > >
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> >
> > --
> >
> --------------------------------------------------------------------------
> > Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> > Phone: +43-1-58801-165300
> > Email: peter.blaha at tuwien.ac.at <mailto:peter.blaha at tuwien.ac.at>
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> --
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-165300
> Email: peter.blaha at tuwien.ac.at WIEN2k: http://www.wien2k.at
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