[QE-users] Regarding bands

[Satyasiban Dash ph19d005]

Thank you for your response.

On Thu, 28 Apr, 2022, 5:57 pm Giuseppe Mattioli, <
giuseppe.mattioli at ism.cnr.it> wrote:

>
> Dear Satya
>
> Like Giovanni, I also don't know why you don't obtain what you expect.
> But I want to offer my own penny to the discussion.
>
> 1) Due to the well known effect of delocalization errors in GGA-DFT,
> the band gap of Si is generally reduced to around 0.6 eV. The
> reduction involves both the lowering of the conduction band potential
> and the raising of the valence band potential. In the case of ZnO you
> have a strongly curved conduction band around the minimum at Gamma,
> which is not affected by delocalization errors, and a very problematic
> valence band, in which the interaction between the narrow O 2p and Zn
> 3d contributions may raise the valence band maximum by more than 2 eV,
> shrinking the band gap to less than 1 eV in bulk ZnO.
>
> 2) First of all, therefore, I would check *in the same supercell* if
> isolated Si and isolated ZnO slabs envisage a metallic character of
> the junction due to the unsymmetrical band gap underestimation of the
> two parts.
>
> 3) The most stable ZnO surface is (10-10), not 0001 (or its 000-1
> counterpart having reverse polarity). The polar surfaces of ZnO are
> tricky to simulate as slabs due to the strong polarity of the Zn-O
> bond. In the past, I obtained some weird layered hexagonal structure
> similar to BN! I suppose that the choice of (0001) is purposeful. If
> it is not, try to reconsider your choice.
>
> 4) Such a strongly polar surface in contact with a non-polar Si
> surface may induce a huge interfacial charge transfer, even enhanced
> by delocalization errors mentioned above, or can lead to significant
> shifts of band edges, yielding a metallic character of the
> semiconductor junction.
>
> HTH
> Giuseppe
>
> Quoting Satyasiban Dash ph19d005 <ph19d005 at smail.iitm.ac.in>:
>
> > Yes . Thank you for the clarification. I am trying to match (0001)
> surface.
> > But I have observed upon relaxing ZnO loosing its symmetry and this may
> be
> > due to the polar surfaces but experimentally we do observe a band gap. I
> > have also tried dipole correction but results are same. But if I remove
> Si
> > its giving a gap. Is there anyway to reproduce it with Si (001).
> >
> > On Thu, 28 Apr, 2022, 4:55 pm Giovanni Cantele, <
> > giovanni.cantele at spin.cnr.it> wrote:
> >
> >> Dear Satya,
> >>
> >> it is not that easy (at least for me) to provide an answer to your
> >> question using the data you have provided. Maybe the output files (of
> scf
> >> and bands) and a plot of your band structure might help to infer if
> there
> >> is any issue in your calculation.
> >>
> >> However, before wondering whether you get a metal whereas experiments
> >> measure a gap, you should also check that you are simulating a system
> that
> >> is as close as possible to the experimental one (in terms of thickness
> >> and/or surface orientation of both ZnO and Si, and so on). As far as the
> >> atomic positions are concerned, they look reasonable. It seems (if I’m
> not
> >> wrong) that you are trying to match a Si(100) surface with a ZnO(0001)
> >> surface, aren’t you? Is this what you expect?
> >>
> >> Giovanni
> >>
> >> --
> >>
> >> Giovanni Cantele, PhD
> >> CNR-SPIN
> >> c/o Dipartimento di Fisica
> >> Universita' di Napoli "Federico II"
> >> Complesso Universitario M. S. Angelo - Ed. 6
> >> Via Cintia, I-80126, Napoli, Italy
> >> e-mail: giovanni.cantele at spin.cnr.it <giovanni.cantele at spin.cnr.it>
> >> Phone: +39 081 676910
> >> Skype contact: giocan74
> >>
> >> ResearcherID: http://www.researcherid.com/rid/A-1951-2009
> >> Web page: https://sites.google.com/view/giovanni-cantele/home
> >>
> >>
> >> On 28 Apr 2022, at 07:09, Satyasiban Dash ph19d005 <
> >> ph19d005 at smail.iitm.ac.in> wrote:
> >>
> >> Dear Users
> >>  I have been trying to calculate a heterostructure with a slab model. I
> >> have followed most of the examples given in the forum and tried it
> still I
> >> am getting a metallic band structure. I have used the K-path generation
> >> tool provided in "material project" website  to generate k-path. I have
> >> given the scf and bands.in file as attached files. Please have a look.
> >> Experimentally this system has a wide band gap.
> >>
> >>
> >> Thanks.
> >> Satya
> >> Research Scholar
> >> IIT Madras.
> >> <scf.in><job576185.pw.in
> >_______________________________________________
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> >> and economic cooperation amongst peoples
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>
>
> GIUSEPPE MATTIOLI
> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
> Via Salaria Km 29,300 - C.P. 10
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> E-mail: <giuseppe.mattioli at ism.cnr.it>
>
> _______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
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