[Wien] Ghost band error in SnS2 continued....

[shamik chakrabarti]

Dear Prof. Laurence, Prof. Gerhard & Prof. Peter,

                                  Thank you so much for your valuable
advices. I will try all the options & will let you know the results within
a few days.

with best regards,

On Wed, 29 Jan 2020 at 00:59, Peter Blaha <pblaha at theochem.tuwien.ac.at>
wrote:

> First of all, the VASP gaps of bulk SnS2 are 1.91 eV, not 2.1 as you are
> writing ?????
>
>
> Then there are other VASP papers, which report different results, in
> particular different structural parameters:
>
> (Phys. Chem. Chem. Phys., 2016, 18, 318)
> a=3.693 c=11.680   gap:   1.91
>
> https://doi.org/10.1016/j.actamat.2014.03.042:
> a = 3.518 Å, c = 5.844 Å),  gap 1.92 eV  (also PBE+U(9 eV !!
>
> SnS2 is a layered material and all VASP papers used a DFT-D2 (+U)
> approach. It could be that your Sn position is quite different from
> theirs ???
>
> PS: I would not reduce the RMTs. You will make the effect of U even
> smaller with smaller RMTs.
>
> PPS:
> I'd use TB-mBJ or hybrid-DFT for band gaps- but you said, band gaps are
> not your focus, but the voltage of LiSnO2.
>
> For this you need good structural parameters AND good cohesive energies.
>
> I'd use a vdW-functional (for instance rev-vdW-DF2, see our paper) to
> optimize the structure and also the SCAN meta-GGA for the energies (the
> formation energy determines the Voltage).
>
>
> On 1/28/20 3:11 PM, shamik chakrabarti wrote:
> >
> > Dear  Professor Laurence and wien2k users,
> >
> >                                        with reference to my earlier mail
> > on SnS2, I have checked the change in RMT (for avoiding Ghostband) with
> > U and corresponding band gap. The details are as follows;
> >
> > U = 7 eV      RMT reduction 6%     Band gap = 1.460 eV
> > U = 8 eV      RMT reduction 15%    Band gap= 1.475 eV
> > U= 9 eV       RMT reduction 30%    Band gap = 1.512 eV
> >
> > I have not able to reproduce the band gap ~ 2.1 eV as computed
> > earlier using Vasp (Phys. Chem. Chem. Phys., 2016, 18, 318). Also,
> > whether 30% reduction of RMT  is acceptable???
> >
> > Looking forward to further guidance from you.
> >
> > with regards,
> >
> > --
> > Dr. Shamik Chakrabarti
> > Research Fellow
> > Department of Physics
> > Indian Institute of Technology Patna
> > Bihta-801103
> > Patna
> > Bihar, India
> >
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> >
>
> --
>
>                                        P.Blaha
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
> Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
> WWW:   http://www.imc.tuwien.ac.at/TC_Blaha
> --------------------------------------------------------------------------
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-- 
Dr. Shamik Chakrabarti
Research Fellow
Department of Physics
Indian Institute of Technology Patna
Bihta-801103
Patna
Bihar, India
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