Carbon nanotube

See also

BAND-NEGF Documentation

Let us begin by modeling the electron transport through a carbon nanotube:

/scm-uploads/doc.2017/Tutorials/_images/negf_t1_system_setup.png

Setting up the system

Start up ADFInput
1. Switch to BAND
2. Select Task → NEGF
3. Click on MoreBtn to switch to the NEGF panel (or click on Model → NEGF)
/scm-uploads/doc.2017/Tutorials/_images/negf_t1_main_panel.png

From the NEGF panel we can set up the geometry of our system and specify various NEGF calculation parameters:

We first need an .xyz file defining our lead, that is, a carbon nanotube:

Click here to download the .xyz file carbon_nano_tube_4-4.xyz

We now import our lead:

1. Click on the folder icon next to Lead: this will prompt a file dialog window
2. Open carbon_nano_tube_4-4.xyz (the .xyz file you just downloaded)
/scm-uploads/doc.2017/Tutorials/_images/negf_t1_select_lead.png
Set Lead Repetitions to 2

Note

The leads cannot be directly modified in the molecule-editing area. In the next tutorial we will show how to create a leads.

We now need to define our central region. In this tutorial, the central region consist of a nanotube (same as in the lead). We can easily fill in the central region with lead-material with the Fill central region option:

1. Click on Fill
2. Enter 2 in the prompted dialog window and click on OK
/scm-uploads/doc.2017/Tutorials/_images/negf_t1_fill_with_bulk.png

This concludes the geometry-building part of a NEGF calculation. Your system should look like this:

/scm-uploads/doc.2017/Tutorials/_images/negf_t1_geo_ready.png

Running the calculation

From the NEGF panel we can change other NEGF parameters, but in this tutorial we will use the default values.

Important

In this tutorial we use the Non self consistent NEGF method. This method represents a computationally cheap alternative to the more sophisticated self consistent method, but it can only be used for zero-bias calculations. See the BAND-NEGF Documentation for more details.

We are ready to run the calculation:

Note

The following calculation could easily take more than 10 minutes on a desktop machine.

Click on File → Save as...
Run the calculation with File → Run
Wait for the calculation to finish

Visualizing the results

The results can be visualized with ADFSpectra. To start up ADFSpectra:

Click on SCM → Spectra...

Here you can visualize:

  • Transmission function \(T(E)\)
  • NEGF-DOS (density of states)
  • Current v.s. Bias Potential (computed from the the zero-bias Transmission function)
In ADFSpectra, click on Spectra → Transmission / Transmission+DOS / Current

Note

Energies are relative to the Fermi energy of the lead, i.e in the picture below, 0 eV corresponds to the Fermi energy of the nanotube (first simulation in Simulations work flow)

This is the transmission function of our nanotube:

/scm-uploads/doc.2017/Tutorials/_images/negf_t1_transmission.png