Tutorial D1-3
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Transmission spectrum of a graphene nanoribbon with a distortion Transmission spectrum of a graphene nanoribbon with a distortion
The device system
In this tutorial, you will study the electron transport properties of a graphene nanoribbon with a distortion. You will be introduced to device geometries and different analysis tools for investigating the electronic transport properties of devices.
Start by opening VNL. In the VNL top menu select Projects, and open the ExampleProject. The example project has a number of result files, in the ExampleProject
following you will be examining the “” result file. Expand the nanoribbon_ivcurve entry and select the device configuration (object
< This will display the configuration in a gID000). In the right panel
3D graphics window.
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The structure is a so called device geometry
device geometry. It consists of three parts: the left electrode, the central region, and the right electrode. The left and right electrodes are semi-infinite periodic in the negative/positive Z direction, the transport direction. The electrodes may differ from one another, e.g. be composed of different materials or have different structures. However, they must be periodic, and they must have a common unit cell in the X/Y plane. For more details about how to set up a device configuration, go to the tutorial Building a graphene nanoribbon device.
The central region consists of extension copies of the two electrodes and a scattering region in between, as depicted in the figure below. Here, the vectors A, B, and C span the electrode. For device simulations, the C-vector must always be parallel to the Z axis, and the AB-plane must be orthogonal to the Z axis.
The configuration also has an attached calculator. To see the details of the calculator, select the device configuration (object gID000), and open the general info plugin. You will notice that a selfconsistent Huckel method was used for the calculations. A Cerda and a Hoffmann basis set was set for Carbon and the Hydrogen, respectively.
In the following you will learn how to perform an IV Curve calculation for the system. Building the graphene nanoribbon device is explained in this tutorial. Calculating the I-V curve
You will now calculate an I-V curve for the nanoribbon device. To this end you will need to perform a selfconsistent calculation and calculate the transmission spectrum for each bias in the I-V curve. From the transmission spectrum it is then possible to calculate the current at each bias, thereby obtaining the I-V curve. In the following you will set up an I-V curve calculation by using the I-V curve
object in ATK. This object automatically sets up the bias loop and calculates the transmission spectrum for each bias in the I-V curve.
Script Select the device configuration (gID000), drag and drop it onto the Script Generator icon  in the VNL tool bar.
Generator
This will open the scripter with the device configuration and the attached calculator. Now add the following analysis objects:
1. Analysis -> TransmissionSpectrum
2. Analysis -> IVCurve
3. Change the default filename to “”
!Tip
Script panel If you insert the wrong block by mistake, you can select it in the Script
and press Delete on the keyboard to remove it. The inserted blocks in the script can also be reordered by dragging them up or down.
Now you need to make sure that each script block is set up properly.
Double-click the  block in the Script
parameters, for instance the Huckel basis set used for the calculation.

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