Mailman 3 January 2019 - Kwant-discuss

Datta’s ballistic transport formalism vs KWANT
by mutcran Jan. 22, 2019

Jan. 22, 2019

Hi, I tried to compare KWANT’s results for transmission with Datta’s ballistic transport formalism where total transmission is written as Ttot=T(E)M(E) Here Datta takes T(E)=1 for ballistic transport (please see: J. Appl. Phys. 105, 034506, 2009) and M(E) is the number of modes in transverse direction. When I compared KWANT's results with Datta’s expression, for the system given in “quantum_wire_revisited.py”, I found different results (please see the attached figure where I tried to put every relevant thing in the calculation). Since the reflectance is zero for that system and so transmission is 1 for each mode, shouldn’t it give the same results with Datta’s transmission expression? Best, Ran �

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Error in bounds keyword in kwant.kpm.spectraldensity
by Hadi Zahir Jan. 15, 2019

Jan. 15, 2019

Dear all, I receive the following error when I call kpm.spectraldesnisty with a "bounds" keyword. Here is the error: in _rho = kwant.operator.Density(syst, sum=True, where=in_circle, bounds=[lw_bound, up_bound]) File "kwant/operator.pyx", line 735, in kwant.operator.Density.__init__ TypeError: __init__() got an unexpected keyword argument 'bounds' I do not provide my own code since I think this is a kwant internal error. Thanks and best regards,Hadi

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Using the energy eigenvalue spectrum for conductance
by mutcran Jan. 13, 2019

Jan. 13, 2019

Hi, For the calculation of the conductance in the tutorial file “quantum_wire_revisited.py”, instead of giving arbitrary energies like [0.01 * i for i in range(100)], can I give the real energy values of the system by: E=(pi^2*hbar^2)/(2m)*(nx^2/L^2+ny^2/W^2) where I took transport direction length (L) as very long, say 100 times larger than the width (W). (Since the transport direction is practically open in KWANT) This gives very different results than using arbitrary energies. What is the problem with this approach and is there a way to explicitly account the discrete energies of the system (not the arbitrary ones)? Best, Ran �

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Number of modes calculation
by mutcran＠mynet.com Jan. 7, 2019

Jan. 7, 2019

Hi, I am trying to calculate conductance for a simple 2D nanowire with length L and width W by using the following formula: G=(2e^2/h)*Integrate[T(E)M(E)(-df/dE),dE] My questions are these: 1- Does KWANT include the number of modes, M(E), inside the transmission function or not. In other words does “smatrix.transmission(1,0)” contains only T(E) or M(E)*T(E) ? 2- If it does not include it, should I calculate the number of modes from the band structure of the leads? If it includes the number of modes, does it uses Heaviside(E-e1) or W*sqrt(2m(E-e1))/(pi*hbar)? It may be a very simple question, I tried to understand it from tutorial but it doesn’t mention “the number of modes” concept at all in the calculation of conductances. I’d appreciate any clarification. Best, Ran �

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Install Kwant on Win 10
by Zhanzhi Jan. 4, 2019

Jan. 4, 2019

Hi, I am trying to install Kwant on a Win 10 PC. I followed the steps https://kwant-project.org/install but cannot finish the final step successfully. The command window says “no module named pip” after I execute python -c "import pip, glob; pip.main(['install', '--no-deps'] + glob.glob('*.whl'))" and “python3 is not recognized as an internal or external command, operable program or batch file” after I execute python3 -c "import pip, glob; pip.main(['install', '--no-deps'] + glob.glob('*.whl'))" What is the possible problem? Best, Zhanzhi Sent from Mail for Windows 10

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Problems of Running kwant.ldos(sys, 0.2) and kwant.plotter.map(sys, ldos)
by Zhanzhi Jiang Jan. 1, 2019

Jan. 1, 2019

Hi, I am following the vedio tutorial provided by Christoph ( https://kwant-project.org/doc/kwant-screencast-2014) When I run ldos = kwant.ldos(sys, 0.2) There is an error "TypeError: Expecting an instance of System" Then when I run kwant.plotter.map(sys, ldos) There is an error "NameError: name 'ldos' is not defined" So I cannot get the map of the local DOS as shown in the vedio. It looks like the second error is a result of the first one. How could I solve this? Best, Zhanzhi

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