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811

Scripts, Tutorials and Applications / Script for calculating the voltage drop.

« on: December 17, 2008, 23:12 »

Hey everyone.

I just thought I wanted to share with you a small script for calculate the voltage drop using two selfconsistent calculations
on a twoprobe device.

The usage is straight forward:
1)  perform a calculation of a twoprobe at zero bias and store the results in a netcdf file.
2) Do the same for the finite bias, and store this in another netcdf file.
3) Modify the script to match the names of your two calculations, and run it using atk voltagedrop.py.

Then you are done, and you will recieve the voltage drop in a VNL file for visualization in VNL and the
average voltage drop will be printed to the screen. Alternative you can pipe the screen into a log file and plot it using fx GNUplot.

I have attached the script and I have attached a graph showing the voltage drop calculated using this script for a Li-H2-Li system.

812

General Questions and Answers / Re: Current calculation comparison with Smeagol

« on: December 11, 2008, 12:44 »

When the electrode unitcell is too short, you will always have scattering - even in a perfect system.
The surface green function used for calculating the self-energies is calculated under the assumption (in ATK)
that it should only consider contribution for the the nearest neighbour unitcells. However if the electrode
unitcell is very small, it will interact with more unitcells and hence this assumption gives rises to a small error,
that will lead to scattering for inbound electrons.

I have attached a small script for illustrating this problem and feel free to play around with it.

I have also attached a small graph of some of the results for a specific perfect chain.
In this case it is clear that if you use a 2-layered electrode, you will have scattering in a perfect system,
and if you use 3-layered electrodes you will not.