MoS2 nanowire

[ramkrishna]

I am not getting any response. Please help me.

[zh]

I have done the band structure calculation with that builder scripts using Huckel as well as DFT with k points (11X11X11), but I can't get any significant change between bulk, 1-layer, 2-layer band structure. According to the literatures( like http://pubs.acs.org/doi/abs/10.1021/nl903868w ) there should be a drastic change between these and the 3, 4-layers do not show any band structure at all. Please help me.   

If possible, please upload the script files for the band structure calculations of 3layers and 2 layers of MoS2.

Since the Huckel method is empirical, the accuracy for the band structure of MoS2 may depends strongly on the used parameters. The meaningful thing is to the DFT calculations for the band structure in order to to compare it with the results in literature.

[ramkrishna]

Dear Sir,
       I have done the band structure calculation for 2 layers and 3 layers using the following attached scripts.

Regards
Ramkrishna

[Anders Blom]

For your 3-layer structure, you have computed the band structure between Gamma and Z, but your system is not periodic in this direction (or rather, there is a big vacuum gap), so naturally there is no dispersion at all. If you want the band structure in the plane of the MoS2 you should keep the structure hexagonal and use the same route as for the other calculations, i.e. between G,K,M.

For the bilayer structure I suspect the results will depend strongly on the distance between the layers. How did you determine that?

[ramkrishna]

I don't know exactly how to measure the distance between the layers in ATK. In the builder I just use (Transform -->repetition) to get that builder files. In literature the distance between the layers is shown 6.5 Angstrom and I thought that just doing repletion only it maintains that distances. Can you please let me know how can I measure interlayer distances and how can I change that also?   

[zh]

The atomic layer distance can be adjusted easily by modifying the z coordinates of atoms. On the other hand, the atomic layer distance can be measured by numerical operation of the z coordinates of Mo atoms in two neighboring layers.

[ramkrishna]

Thank you for your kind reply. The DFT calculation gives proper curvatures of bands for bulk but the indirect band gap (~0.80 eV) is quite lesser than the band gap which is mentioned in the literatures (~1.2eV). On the other hand Huckel method is giving totally wrong band structure. So, to achieve that band gap what modification should I do for the band structure calculation. Attached please find the file for DFT calculation.   

[zh]

Some comments to the setup in your script file:
1). The k-mesh is not set properly. The size of k-mesh should be properly scaled according to the length of the lattice vectors. Since the lattice constant c is roughly 4 times larger than the lattice constant a,  the size of k-mesh along the kz  direction should be smaller than the one along the  kx and ky direction.  So, "k_point_sampling=(11, 11, 3)," may be more reasonable than "k_point_sampling=(11, 11, 11)".
2). To  reproduce the results in literature properly, one had better choose the same exchange-correlation functional with the one used in literature, use the more accurate basis set such as DZP. In addition, the same structural parameters should be used.  

[Anders Blom]

To be clear, using 11 points in Z for this system is not wrong, it just takes extra time without perhaps improving the accuracy (although this should be checked). The script you attached is using the DoubleZetaPolarized basis set, since that's the default.