Script for creating nanotubes

[Anders Blom]

There is no real difference between screening layers and central region layers in this case, so just use the repetition factor the central region.

[serhan]

Thanks, I've posted from my friends's computer thus the user name was different on the above post...

Thanks again.

Cheers,
Serhan

[serhan]

Hi,

I've made a (6,6) CNT with the script provided in this thread. I've plotted its voltage drop along z-direction. Attached is this Figure. However, I'm surprised that a voltage drop also occurs in the electrodes (the first and last 0.9nm correspond to the electrodes). Is this true? Does ATK take the voltage drop in the electrodes into account? Or am I missing something?

Cheers,
Serhan

[Nordland]

Well it is not into the electrode entirely. When ATK performs a twoprobe calculation, it does on a system formed by adding an electrode repetitions ( I call this the padding layers ) to each side of the scattering region. All real space properties are calculated in this region, and hence the voltage drop will be allowed to vary in the padding layers. So it is not in the electrode, but in the extra repetitions of the electrode.

[Anders Blom]

Although, from the user's perspective of how the geometry is defined, it is the electrode

For definiteness, the system which ATK actually performs the calculation on, looks like

L-LP-C-RP-R           (p for padding)

where C=central region and L/LP and R/RP are the left and right electrode geometries. During the self-consistent two-probe calculation, the real space quantities in L and R are fixed to their bulk values, while those in LP and RP are allowed to vary.

So, again, from the perspective of how the system is defined (names of variables etc), the system is L-C-R, and the real space density and effective potential vary freely across this region.

[serhan]

Thanks again 

OK, the voltage drops in the padding layers (as you've shown it as LP ans RP). However, the drop also occurs in L and P, is it right?

Cheers,
Serhan

[Nordland]

The drops does not occour in L and R.

[Anders Blom]

I guess you meant R, not P.

Just to be clear: padding is NOT the same thing as screening. The screening layers are part of C.

Again, from the perspective of how you set up the geometry, you specify to the program a "left electrode", a "right electrode", and a "central region" geometry. These are L, R, and C, and they are stitched together as L-C-R. The voltage drop etc occurs over this region. The whole padding idea is really just related to how the code handles things internally.

[serhan]

Thank you very much,

Cheers,
Serhan