A logical approach seems to be to first make a hexagonal sheet, just like graphene, and then wrap it into the shape of a tube. Indeed, such a tube wrapper plugin has been developed, and in this tutorial you will learn how to use it to build MoS2 and other transition metal sulfide TS2 nanotubes (T = W, Nb, Re), see Refs. [KZH11] and [STT+00].
The recipe is simple enough:
- Create a bulk crystal of MoS2.
- Change it into a monolayer.
- Wrap it using the tube wrapper plugin.
This approach can then easily be adapted for other TS2 structures.
- Step 1: Start VNL and open the AddOn Manager . Scroll down until you find the TubeWrapper addon, and install it. Restart VNL to activate the new addon.
- Step 2: Click ). Use the mouse to select and delete the three atoms to the right in the cell. This leaves a single layer of MoS2. The cell is hexagonal cell, but to make the tube it is necessary to have an orthorhombic supercell to work with. Therefore, open and use the settings illustrated below. and locate molybdenite. Add it to the Stash (clicking
- Step 3: Open . You now have two choices: Repeat in A or B – this will give either armchair (A) or zigzag (B) tubes. Repeat some decent number, like 20 – the new size of the system in the repeated direction will directly determine the circumference of the tube.
If you repeated in A, useand click A<->B then X<->Y to reorient the system. If you repeated in B, skip this step.
- Step 4: Using , click C<->A then X<->Z (do this regardless of whether you repeated in A or B):
- Step 5: Open and select Cartesian coordinates. Then change the first cell vector A so that the size of the cell in X is at least as large as in Y. Open and center the system.
- Step 6: Finally, open the plugin you just installed, and wrap the tube. You can use 360 degrees directly to get a fully wrapped tube, or perhaps 180 degrees for some interesting novel work!
- Step 7: In the end, it’s a good idea to adjust the cell size (it was necessary to keep it large during the building procedure) and then center the system in A and B and afterwards repeat in z direction:
What’s next? Now you can perform calculations on MoS2 nanotubes just as easily as CNTs. The DFTB model used in Ref. [STT+00] is also available in ATK, and you can request the Mo/S parameters from DFTB , and run ATK with those. How to install DFTB parameters is described in another tutorial: DFTB model in ATK .
You can of course also use the method outlined here to make carbon nanotubes, even though the dedicated pluginis much faster to use for a perfect, simple CNT. An interesting example where the Tube Wrapper plugin is anyway useful also for CNTs is for the creation of Stone–Wales defects, which are much easier to define in for a mololayer sheet than for the rolled-up tube. Or, you can make “open” or partially wrapped nanotubes.
|[KZH11]||A. Kuc, N. Zibouche, and T. Heine. Influence of quantum confinement on the electronic structure of the transition metal sulfide ts2. Phys. Rev. B, 83:245213, Jun 2011. doi:10.1103/PhysRevB.83.245213.|
|[STT+00]||(1, 2) Gotthard Seifert, Humberto Terrones, Mauricio Terrones, Gerd Jungnickel, and Thomas Frauenheim. Structure and electronic properties of mos2 nanotubes. Phys. Rev. Lett., 85:146–149, Jul 2000. doi:10.1103/PhysRevLett.85.146.|