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 < [email protected]> 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 <[email protected]>: > > > 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 > > <[email protected]> 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 [email protected] > >> https://lists.quantum-espresso.org/mailman/listinfo/users > > _______________________________________________ > > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > > users mailing list [email protected] > > 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: <[email protected]> > > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users >
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