Carbon nano-tube I-V plot

[Zubair]

I am simulating (13,0) CNT with periodic boundaries using ATK-SE extended Huckel method. I want to see the effect of length on conductance. The I-V curves were formed using voltages from 0 to 0.05 with 0.01 step. I have used two simulations, one with 3 repetitions and another with 22 repetitions of (13,0) unit cell. The expected results were surprising as there was negligible difference between the two curves.

For 3 repetitions:
Voltage list (Volt)
[ 0.    0.01  0.02  0.03  0.04  0.05]
Current list (nano Ampere)
[  0.00000000e+00   1.29796535e-03   5.68050799e-04   8.73723958e-04
   1.20616691e-03   1.57429505e-03]


For 22 repetitions:
Voltage list (Volt)
[ 0.    0.01  0.02  0.03  0.04  0.05]
Current list (nano Ampere)
[ 0.          0.00132664  0.00056978  0.00088076  0.00122454  0.00161345]

My question is:
1) Why are they not different?
2) Why the rise and fall in curve?

I checked the molecular energy spectrum, considering the spectrum as sequential tunneling between the source and drain and the inner region as consisting of discrete molecular orbitals, but this idea does not go well with the spectrum. As according to the molecular spectrum, the I-V should be very much distinct.

Kindly need your help in this regard. Thanks.

[Zubair]

The script for I-V calculation is same as that used in tutorial "li-h2.nc" "Performing an I-V scan with scripting".

[Anders Blom]

The electron transport mechanism in ATK is coherent ballistic, in which case the conductance which doesn't change with the length of the system if the system is perfectly periodic. So your results are perfectly expected.

[Zubair]

Sorry to bother you again, but why is the non-uniformity in I-V curve and the molecular spectrum.

[zh]

Sorry to bother you again, but why is the non-uniformity in I-V curve.

This may be because the CNT(13,0) is a semiconductor.