how to make rectangular nanowire?

[ramkrishna]

I want to make rectangular Silicon nanowires (SiNW) having 10 nm length and 2X3 nm^2 cross-sectional area along <100> direction. Can anyone help me  to make such a system??

[kstokbro]

use the nanowire builder in the custom builder and set the (100) surface energy to 0.1
Remember to passivate the wire with the sp3 passivater which can be found under scripts

[ramkrishna]

Dear Prof Stokbro,
Please let me know how is the surface energy in nanowire window related to the length , cross sectional area ?  In the nanowire Wulff constructor window, how the radius slot is affecting the length and breadth ? how can I specify the dimension of the rectangular nanowire?

thanking you,

Ramkrishna

[ramkrishna]

Dear Sir,
   Please let me know the answers to the above questions.

Thanking you,
Ramkrishna

[Anders Blom]

If you increase the radius, the wire cross-section becomes larger. The surface energies, or rather their relation to each other, determine the shape.

[ramkrishna]

Dear Sir,
     Thank you for your valuable answers but how can I specify the dimension of the rectangular nanowire in this procedure?

Regards
Ramkrishna

[Anders Blom]

I guess you are referring to, how you can make it rectangular rather than quadratic. Well, you can't, the tool in it's current design will only generate regular structures. One alternative is to build a 1x1 nm^2 shape and "glue" them together, 2x3. If you use a metallic material or Si or Ge, you could use the EMT or Brenner potentials in ATK-Classical to optimize the so-obtained geometries. Or build a 3x3 nm^2 structure and remove 1 nm in one dimension.

[ramkrishna]

Dear Sir,
     Can you please let me know the procedure of making a 1X1 nm^2 Si wire ? Eagerly waiting for your answer.

Regards
Ramkrishna

[Anders Blom]

radius 5 Å, 100 surface energy 0.1

[ramkrishna]

Dear Sir,
      To get 2X2 nm^2 should we have to double the radius only or change has to be made in surface energy also?

Regards
Ramkrishna

[Anders Blom]

As mentioned already above, the surface energy controls the shape, not the size. The exact number for the radius if you want 2 nm may not be exactly double, but close.

[ramkrishna]

Dear Sir,
     Thank you for your valuable reply .

Regards
Ramkrishna

[ramkrishna]

Dear Sir,
   I have made a hydrogen passivated rectangular Silicon nanowire along (100) with surface energy 0.1  and radius 1.5nm. Attached please find the file.
After running using Extended Huckel method, I find the direct band gap very close to zero. [Direct Band gap          0.0023 eV at [0.0000, 0.0000,0.4114] ]. However we know from theory that the direct band gap should be of the order of 3-4 eV .

Please let me know if there is any mistake in my model.

Regards
Ramkrishna

[Anders Blom]

Why do you have (4x4) k-points in X/Y? A more proper k-point sampling would be 1x1x100. Also, why limit the number of iterations to 10? Are you sure it even converged? Do you have a reference for the "theory" value of the band gap? (I formulate my answer as a few questions, because you really need to think about these things, and understand the basics.)

[ramkrishna]

Dear Sir,
     I have done as per your previous suggestion but I still get very low band gap (almost zero). Please see the following file and FIG 2 of this given link of a journal paper http://prb.aps.org/abstract/PRB/v76/i15/e155435.

Regards
Ramkrishna