ATK教程：石墨烯納米帶的透射譜計算

1、Tutorial D1-3Docs Tutorials 1D nanostructures Transmission spectrum of a graphene nanoribbon with a distortion Transmission spectrum of a graphene nanoribbon with a distortionThe device systemIn this tutorial, you will study the electron transport properties of a graphene nanoribbon with a distortio

2、n. You will be introduced to device geometries and dierent 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 les, in the ExampleProjectfoll

3、owing you will be examining the “nanoribbon_ivcurve.nc” result le. Expand the nanoribbon_ivcurve entry and select the device conguration (objectViewer. This will display the conguration in a gID000. In the right panel bar Viewer.3D graphics window.The structure is a so called device geometrydevice g

4、eometry. It consists of three parts: the left electrode, the central region, and the right electrode. The left and right electrodes are semi-innite periodic in the negative/positive Z direction, the transport direction. The electrodes may dier from one another, e.g. be composed of dierent materials

5、or have dierent 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 conguration, go to the tutorial Building a graphene nanoribbon device.The central region consists of extension copies of the two electrode

6、s and a scattering region in between, as depicted in the gure 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 conguration also has an attached calculator. To se

7、e the details of the calculator, select the device conguration (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 Homann basis set was set for Carbon and the Hydrogen, respectively. In the following you w

8、ill 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 curveYou will now calculate an I-V curve for the nanoribbon device. To this end you will need to perform a selfconsistent calculation and calcul

9、ate 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 automat

10、ically sets up the bias loop and calculates the transmission spectrum for each bias in the I-V curve.Script Select the device conguration (gID000, drag and drop it onto the Script Generator icon in the VNL tool bar.GeneratorThis will open the scripter with the device conguration and the attached cal

11、culator. Now add the following analysis objects:1. Analysis - TransmissionSpectrum2. Analysis - IVCurve3. Change the default lename to “nanoribbon_ivcurve1.nc” !TipScript panel If you insert the wrong block by mistake, you can select it in the Scriptand press Delete on the keyboard to remove it. The

12、 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 Scriptparameters, for instance the Huckel basis set used for the calculation.Job Manager You may now execute the calculat

13、ion by sending the script to the Job Manager Send to icon . The job will take several hours to complete but only using the Send toaround 1 hour if you use 4 MPI processes. In the following you can investigate the precalculated data available in the examples directory.The I-V curveGo back to the VNL

14、main window. Select the nanoribbon IVCurve objectIV-Plot tool in the Panel bar.(gID002 and open the IV-PlotCheck the box next to Additional plots. I-V plot. The rightmost windows shows the transmission spectrum (top and spectral current (bottom for each bias point, where the blue part of each curve

15、shows the bias window. For each transmission spectrum the electrical current is shown in the topmost middle plot (IV. Placing the mouse curcer over one of the points in the IV or dI/dV plot will highlight the corresponding transmission and spectral current plots.The tool shows all the transmission s

16、pectra and spectral currents and the corresponding I-V points. By hovering the mouse over an I-V point, the corresponding transmission spectrum is highlighted. To calculate the current itis necessary to specify the electron temperature in the electrodes, if the electron temperature is changed the cu

17、rrents are recalculated.The I-V points are connected through a spline interpolation, and the distance between the interpolated points is determined by the step size. The lower plot shows the dI/dV as obtained by dierentiating the spline interpolation.For a system with inversion symmetry, or mirror s

18、ymmetry in the z-direction, the I-V curve will be symmetric in the applied bias. For such systems you can obtain the full I-V curve by only performing the I-V scan in one bias direction. If Symmetrize, the positive bias points will be copied to give theyou tick Symmetrizenegative bias points.The tra

19、nsmission spectrumTo view the transmission spectrum object (gID001 in “nanoribbon_ivcurve.nc”,Transmission Analyzer panel bar plugin.select it and open the Transmission Analyzer The left plot in the transmission analyzer shows the transmission spectrum. In the Curves menu, you can select which spin

20、components are shown. For non-polarized calculations, the default is to show the transmission spectrum of the sum of the up and down channel.With the mouse you can select a point in the active curve. This k-dependent transmission for this energy is then illustrated in the right plot.The transmission

21、 eigenvalues and eigenstateFor a given energy (E and k point ( the transport can be described interms of the transmission eigenstates . The transmission eigenvalues andcorresponding eigenstates are conveniently calculated from the transmissionanalyzer.Select in the plot, and in the plot.Press the Ei

22、genvalues button, and the Transmission Analyzer Transmission Analyzer will report thatthere are three eigenvalues: 0.9903, 0.3098 and 0.00344. Next press the Eigenstates button to calculate the eigenstates for the tickedeigenvalues. After a short calculation a menu appears for how to visualize thest

23、ates. Select to visualize them as an isosurface isosurface.In the viewer, select the Properties menu, and set the isovalue to 0.1, youshould then see the following plots.(E ,T (E ,k A k B E =0T (E (,=(0,0k A k B T (,k A k B The eigenstate with a transmission eigenvalue of 0.99 (left plot has equally

24、 large weight close to the left and right electrodes, while the eigenstate corresponding to eigenvalue 0.00344 (top right has essentiall zero weight close to the right electrode. The interpretation of these results is that an electron incomming from the left electrode in the state with high transmis

25、sion eigenvalue (close to unity can easily exit into the right electrode and hence it is declocalized over the entire central region. However, an electron entering in the state with low transmission eigenvalue is almost fully reected by the defect in the middle of the central region and hence it doe

26、snt have any weight close to the right electrode.The transmission pathwaysThe nal analysis you will perform in this tutorial is to calculate the transmission pathways at the Fermi level. This is a visual view of the electron pathways from the left to the right electrode.Open the scripter and1. Add an Analysis from le object