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QuantumATK => General Questions and Answers => Topic started by: chethankumar_m on February 2, 2017, 06:27

Title: MoS2 Bandstructure
Post by: chethankumar_m on February 2, 2017, 06:27

hi,
I have obtained bandstructure for single layer MoS2 in DFT calculation using GGA-PBE exchange-correlation and DZP, I am getting indirect band gap, but for single layer structure, it has to be direct bandgap right. I am attaching the input file and the bandstructure please tell me if anything wrong in the process.

Thank you

Title: Re: MoS2 Bandstructure
Post by: Daniele Stradi on February 2, 2017, 11:37

Strange, the script looks OK, I will test it.
Daniele.

Title: Re: MoS2 Bandstructure
Post by: Daniele Stradi on February 2, 2017, 12:44

You did not set the constrain for the cell relaxation correctly. The correct constrain is:
constraints = [FixStrain(x=False, y=False, z=True)]

I this way the in-plane lattice constant of MoS2 is optimized and the interlayer spacing remains fixed, and you get a direct gap. I attach the plot of the bands and the revised script.   

Title: Re: MoS2 Bandstructure
Post by: chethankumar_m on February 2, 2017, 16:42

Thank you. But if you observe the valence band energy at gamma point has much less value(since it is -ve) compare to k point. I also tried and got the same result but still, it's in indirect band gap only right? is it possible to fix it?

Title: Re: MoS2 Bandstructure
Post by: chethankumar_m on February 6, 2017, 06:03

please observe the zoomed view of the valence band, we should get the maxima at k-symmetry point. but, it is in gamma. how to fix this porblem?

Title: Re: MoS2 Bandstructure
Post by: Daniele Stradi on February 6, 2017, 11:42

I checked, it is related to the actual combination of basis set and pseudopotential that you are using.

You can get a direct band gap monolayer MoS2 either using the LDA xc-functional and the DZP basis set, or using the PBE xc-functional and the OMX-Medium basis set.