[QE-users] Dangling bonds with CdS

[Dr. SUNIL KUMAR]

Thankyou for your explanation regarding Dangling bond.
I have one more question. Is it sufficient to remove one atom Cd (or  S)
form CdS crystal or also i need to modify/regenerate pseudo-potential file
to calculate properties related to Dangling bond during DFT simulation?
thanks
Dr. Sunil Kumar
Ph.D (Chemical Engg. IIT Delhi)
M.Tech (Chemical Engg. IIT Delhi)
B.Tech (Chemical Engg. IET-CSJMU Kanpur)
Scientist-C and Assistant Professor
CSIR-National Metallurgical Laboratory Jamshedpur-831007
http://www.nmlindia.org/
https://scholar.google.co.in/citations?user=OchYqugAAAAJ&hl=en&oi=sra



On Thu, Nov 12, 2020 at 8:53 PM Giuseppe Mattioli <
giuseppe.mattioli at ism.cnr.it> wrote:

>
> Dear Tamas and Kumar
> only to add a few words to the (very pertinent) Tamas' reply:
> 1) Semiconductor surfaces can undergoes very complex reconstruction
> patterns (the 7x7 Si(111) reconstruction being likely the most famous
> case). You will not find complex reconstructions by simply cutting and
> relaxing the slabs, and it is best to search in experimental
> literature, in order not to waste time simulating unphysical systems
> which are never going to converge.
>
> 2) Dangling bonds can be also created inside crystals (e.g, by atomic
> vacancies). It is not clear what kind of dangling bond you are
> referring to.
>
> 3) There is an additional problem when you want to simulate some
> process happening on the surface (e.g., adsorptions of molecules).
> Various strategies can be used, including the saturation of dangling
> bonds on one side of the slab by "pseudohydrogen atoms" having
> fractional charge mimicking that of the pristine bond broken by
> cleavage.
>
> This said, you should "make an educated guess" [cit. John Malkovich
> :-)] and ask less general questions which may (or may not) generate
> more useful answers.
>
> HTH
> Giuseppe
>
> Quoting Tamas Karpati <tkarpati at gmail.com>:
>
> > Dear Dr. Kumar,
> >
> > I guess dangling bonds are written about in DFT textbooks of the
> > physicists' style
> > (in quantum chemistry, ie. clusters rather than crystals, it is less
> > of a problem).
> >
> > The typical problem is that you cut chemical bonds when cleave the
> > crystal (to get a slab).
> > In case of bonds originally dominated by ionic (Coulomb) forces you
> > may still have a closed
> > shell system (ie. just paired electrons) after the cleavage. As for
> > the more covalent
> > bonds, radicals are generated and such high multiplicity electronic
> > states (large
> > magnetizations in terms of QE/PW.x inputs) reorganize to the more
> > stable closed
> > shell systems by changing geometry (you need to reoptimize their
> > geometry) and
> > simultaneously forming new bonds. This way every few surface atom
> > pairs get closer
> > and such bonds form, ie. bonds that were dangling after you made the
> > cut are now
> > in covalent bonds again (no dangling anymore).
> > This you can model by reoptimizing with low (not sure but probably
> > zero) magnetization.
> >
> > CdS has strong bonds carrying both ionic (maybe less) and covalent nature
> > (more of the latter). Depending on the cleaving plane you applied to
> > the crystal,
> > you have a high chance to see new Cd-S bonds form. Less probable is
> > that you'll
> > have Cd-Cd bonds or -S-S- bridges but these are also possible if your
> surface
> > atoms are situated so.
> >
> > Another way of treating such systems is to keep the structure as you
> have cut
> > from the crystal and apply a high starting_magnetization in a PW/relax
> job.
> >
> > Be careful, though, as the chemistries you describe by the above two
> methods
> > (reorganization vs. high magnetization) are living in two distant
> Universes.
> >
> > I hope this helps,
> >   Tamas
> >
> > On Thu, Nov 12, 2020 at 8:13 AM Dr. SUNIL KUMAR
> > <suniliitd14 at gmail.com> wrote:
> >>
> >> Dear QE developers and Users.
> >> I am struggling to carry out a DFT simulation of CdS with dangling
> >> bonds using Quantum Espresso DFT packages. I am unable to
> >> understand the phenomena of Dangling bond and its implementation in
> >> QE DFT simulation. I would like to request to you all, kindly
> >> suggest me some tutorial and sample QE scripts for CdS with
> >> Dangling bonds. I will be grateful to you.
> >>
> >> Thanks
> >> With regards
> >> SUNIL
> >> Dr. Sunil Kumar
> >> Ph.D (Chemical Engg. IIT Delhi)
> >> M.Tech (Chemical Engg. IIT Delhi)
> >> B.Tech (Chemical Engg. IET-CSJMU Kanpur)
> >> Scientist-C and Assistant Professor
> >> CSIR-National Metallurgical Laboratory Jamshedpur-831007
> >> http://www.nmlindia.org/
> >> https://scholar.google.co.in/citations?user=OchYqugAAAAJ&hl=en&oi=sra
> >>
> >> _______________________________________________
> >> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> >> users mailing list users at lists.quantum-espresso.org
> >> https://lists.quantum-espresso.org/mailman/listinfo/users
> > _______________________________________________
> > Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> > users mailing list users at lists.quantum-espresso.org
> > https://lists.quantum-espresso.org/mailman/listinfo/users
>
>
>
> GIUSEPPE MATTIOLI
> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
> Via Salaria Km 29,300 - C.P. 10
> I-00015 - Monterotondo Scalo (RM)
> Mob (*preferred*) +39 373 7305625
> Tel + 39 06 90672342 - Fax +39 06 90672316
> E-mail: <giuseppe.mattioli at ism.cnr.it>
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20201112/7a8adba5/attachment.html>