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

[Peter Blaha]

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
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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