capping nanotubes

[Zexter]

Hi
How to cap a nanotube if i already have a structure of the nanotube with open ends.Is it possible to compute the van der Walls interaction between two such capped nanotube if they are in a close proximity distance.

[zh]

If you use the Virtual NanoLab 2008.10, the "Molecular Builder" is very useful to cap  nanotubes. It can be acheived by manipulating two CNTs as molecules. The correction to the  van der Walls force is not implemented in the available version of ATK, so it is impossible to compute the  van der Walls interaction.

[asmaa]

How can I manipulate two built nanotubes as atoms? can you give me example?

[zh]

1. create a file with the xyz format for the atomic coordinates of CNT;
2. launch VNL and import the obtained xyz file in the 1st step;
3. drop the sample in the 2nd step into the "Molecular builder".
4. import the xyz file of C60 molecule;
5. drop the sample of C60 molecule into the "Molecular builder";
6. manipulate the C60 in the "Molecular builder": remove some of carbon atoms in C60 to prepare the cap; and adjust the position of cap relative to the CNT.

[asmaa]

If you use the Virtual NanoLab 2008.10, the "Molecular Builder" is very useful to cap  nanotubes. It can be acheived by manipulating two CNTs as molecules. The correction to the  van der Walls force is not implemented in the available version of ATK, so it is impossible to compute the  van der Walls interaction.

so after manipulating them, the program will treat them as carbon atoms distributed in different places and get the overall DOS and Bandstructure or we have to include some specific treatment?
Second when you are telling it is impossible to compute the van der waals interaction, you mean that we can not extract the interaction but we can get the overall performance?

[zh]

If two ends of a CNT are capped, the capped CNT can be treated as only a molecule, i.e., the periodicity is removed. Therefore, no band structure is available for such system.
You can obtain the interaction between CNTs, but the contribution from the van der waals interaction is not available using the current version of ATK.

[asmaa]

If two ends of a CNT are capped, the capped CNT can be treated as only a molecule, i.e., the periodicity is removed. Therefore, no band structure is available for such system.
You can obtain the interaction between CNTs, but the contribution from the van der waals interaction is not available using the current version of ATK.

what if they are not capped and infinitly long, can we get the overall band structure?

[zh]

Yes, the band structure can be calculated for infinitely long CNT, since the infinitely long CNT has one-dimensional periodicity.

[asmaa]

Yes, the band structure can be calculated for infinitely long CNT, since the infinitely long CNT has one-dimensional periodicity.

Thank you so much for you fast follow up. How can I know the length of the CNT from z-repitition? for example if I set the z- repitition to be 1, what will be the CNT length?

Another thing, would you please refer me to the tutorial or the forum that explains (from scratch), how can I build two metallic electrods to control the bias voltage over some material?
also can I build four electrod system?
Thanks,
asmaa

[Zexter]

you can see the length by visualizing the lattice, press the lattice button,
or press the z-matrix button, and select two atoms, then you will see the distance between the atoms
     from the post length of the nanotube.

[asmaa]

Thanks a lot Zexter! do you have any idea how to build metallic electrodes? and what if we want to make it from different metal rather than the central area that may contains CNT?