ATK教程：石墨烯納米帶的透射譜計(jì)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 nanorib

2、bon with a distortion. 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 th

3、e ExampleProjectfollowing 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 dev

4、ice geometrydevice geometry. 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 o

5、f dierent materials 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

6、of the two electrodes 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 attach

7、ed calculator. To see 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

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

9、lculation 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.

10、 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 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

11、and the attached calculator. 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 th

12、e 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 Scriptparameters, for instance the Huckel basis set used for the calculation.Job Manager You

13、may now execute the calculation 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

14、I-V curveGo back to the VNL 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

15、the blue part of each curve 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

16、shows all the transmission spectra 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 t

17、emperature is changed the currents 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 inv

18、ersion symmetry, or mirror symmetry 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 Symmetrize

19、negative bias points.The transmission 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

20、, you can select which spin 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

21、 right plot.The transmission 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,

22、and in the plot.Press the Eigenvalues 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 appear

23、s for how to visualize thestates. 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

24、 0.99 (left plot has equally 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

25、the state with high transmission 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 cen

26、tral region and hence it doesnt 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.O

27、pen the scripter and1. Add an Analysis from le object, and select gID000 in“nanoribbon_ivcurve.nc”2. Add an Analysis -> TransmissionsPathways object.3. Change the default lename to “eigenstates.nc” Send the script to the job manager and execute the script. This will take less than a minute.LabFlo

28、or and When the calculation is done expand “eigenstates.nc” on the LabFloorViewer to plot it. The volume of select the transmission pathway object. Press Viewereach arrow indicates the magnitude of the local transmission between each pair of atoms, the arrow and the color designates the direction of

29、 the electron ow.The positions of the atoms are quite obviously deducible, but you can also add them explicitly by dropping the device conguration (gID000 onto the plot. The bonds hide the arrows so the best option is to plot only atoms using radius 0.2, which can be done from the atom tab on the Properties viewer panel bar.Transmis