Mailman 3 October 2015 - Kwant-discuss

How the spin is positioned in the Smatrix?
by Qingtian Zhang 06 Mar '22

06 Mar '22

Dear all, I am trying square lattice with spin-orbit coupling and Zeeman splititng just like the example of Tutorial 2.3.1. Now I want to get the spin-dependent conductance：Guu,Gud,Gdu,and Gdd, where "u" indicates up spin, d indicates down spin. We can have the scattering matrix through Smatrix=kwant.smatrix(sys, energy), but how the spin is positioned in the scattering matrix? I have checked some simple cases, it seems the Smatrix is organized like this: | r t | S= | t' r' | but how the spin is included? Thanks in advance. Qingtiian Zhang The code is: import kwant from matplotlib import pyplot from numpy import matrix import tinyarray sigma_0 = tinyarray.array([[1, 0], [0, 1]]) sigma_x = tinyarray.array([[0, 1], [1, 0]]) sigma_y = tinyarray.array([[0, -1j], [1j, 0]]) sigma_z = tinyarray.array([[1, 0], [0, -1]]) sys=kwant.Builder() lat=kwant.lattice.square() a=1 t=1.0 alpha=0.5 e_z=0.08 W=2 L=2 sys[(lat(x, y) for x in range(L) for y in range(W))] = \ 4 * t * sigma_0 + e_z * sigma_z # hoppings in x-direction sys[kwant.builder.HoppingKind((1, 0), lat, lat)] = \ -t * sigma_0 - 1j * alpha * sigma_y # hoppings in y-directions sys[kwant.builder.HoppingKind((0, 1), lat, lat)] = \ -t * sigma_0 + 1j * alpha * sigma_x #### Define the left lead. #### lead = kwant.Builder(kwant.TranslationalSymmetry((-a, 0))) lead[(lat(0, j) for j in xrange(W))] = 4 * t * sigma_0 + e_z * sigma_z # hoppings in x-direction lead[kwant.builder.HoppingKind((1, 0), lat, lat)] = \ -t * sigma_0 - 1j * alpha * sigma_y # hoppings in y-directions lead[kwant.builder.HoppingKind((0, 1), lat, lat)] = \ -t * sigma_0 + 1j * alpha * sigma_x #### Attach the leads and return the finalized system. #### sys.attach_lead(lead) sys.attach_lead(lead.reversed()) kwant.plot(sys) sys=sys.finalized() print "Hamiltonian=" print sys.hamiltonian_submatrix() Smatrix=kwant.smatrix(sys, energy=3.) print "The scattering matrix=" print matrix.round((Smatrix.data),2) print "T=",(Smatrix.transmission(1, 0))

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How to caculate hall resistance
by ZHANG Bing 12 Sep '21

12 Sep '21

Dear Sir, I am a PhD student of Hong Kong University of Science and Technology. I want to use KWANT to caculate Hall resistance of a Hall bar structure.We can get the conductance between 6 electrodes, but how to get hall resistance? Can you give me some help? Thank you very much. Best Regards, Zhang Bing

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New instructions for Windows installation
by Michael Wimmer 15 Jan '16

15 Jan '16

Dear kwant users, we have posted new instructions for installing kwant on Windows on the kwant website: http://www.kwant-project.org/install The old instructions do not work any more, as the format of the python packages on Christoph Gohlke's webpage have changed. Best regards, the kwant team

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Plot setting
by Weiyuan Tong 09 Nov '15

09 Nov '15

Dear all, I have a question about the figure plotting of kwant, or maybe it is just a python question. When we plot more than one figures in kwant, we need to close the first figure to let the second one start to be plotted. Can we plot all the figures without manually closing the figure window? Maybe a silly question, i am really not good at python. Weiyuan Tong

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QZ Iteration fails
by Maximilian Trescher 09 Nov '15

09 Nov '15

Dear kwant users and developers, this is my first post to this list, I'm a PhD student from Berlin. Currently I'm trying to implement a lattice model of a pyrochlore slab in kwant. I found a (more or less straightforward) way to introduce periodic boundary conditions in the system in the maillinglist archive. This works very nicely as long as I keep the periodicity along a lattice vector. But I run into problems when I choose different directions: Most of the time all solvers fail with a "LinAlgError: QZ iteration failed to converge in zgges". I know about this post http://comments.gmane.org/gmane.comp.science.kwant.user/372 but in my case it occurs not only for a band bottom, but for a range of energies. To give you all the details I prepared a Ipython notebook that you can view here: http://nbviewer.ipython.org/gist/faucon/729050da5e3f2eae1bb8# (Note that the inclusion of complex next-nearest-neighbor hopping is crucial to produce the error, I tried to create the shortest example which reproduces my problem). Do you have any idea how to circumvent this problem? Is it somehow related to http://netlib.org/lapack/Errata/vrac/lapack_known_issues.html#QZ this problem in Lapack? I would be thankful for any hint, Best, Maximilian

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problem loading MUMPS: build.conf?
by Becuwe Stefan 28 Oct '15

28 Oct '15

Hello, I have installed (in non standard directories) * MUMPS 5.0.1 * * SCOTCH 6.0.4 * METIS 5.1.0 resulting in following libs * libcmumps.a libdmumps.a libmpiseq.a libmumps_common.a libpord.a libsmumps.a libzmumps.a * libesmumps.a libptesmumps.a libptscotch.a libptscotcherr.a libptscotcherrexit.a libscotch.a libscotcherr.a libscotcherrexit.a libscotch_group.a * libmetis.a I use Intel’s icc/ifort/MKL. When building kwant, the output shows "User-configured MUMPS", no errors. I use following build.conf file: [mumps] libraries = zmumps mumps_common pord metis esmumps scotch scotcherr mpiseq library_dirs = $MUMPS/lib $METIS/lib $SCOTCH/lib [lapack] libraries = mkl_intel_lp64 mkl_sequential mkl_core mkl_def library_dirs = $IMKL/mkl/lib/intel64 extra_link_args = -Wl,-rpath=$IMKL/mkl/lib/intel64 However, it seems something is going wrong since MUMPS cannot be loaded. I tried both kwant 1.0.5 and 1.1.1. >>> from scikits import umfpack >>> import kwant […]/lib/python2.7/site-packages/kwant-1.1.1-py2.7-linux-x86_64.egg/kwant/solvers/default.py:18: RuntimeWarning: MUMPS is not available, SciPy built-in solver will be used as a fallback. Performance can be very poor in this case. >>> from kwant.linalg import mumps Traceback (most recent call last): File "<stdin>", line 1, in <module> File "[…]/lib/python2.7/site-packages/kwant-1.1.1-py2.7-linux-x86_64.egg/kwant/linalg/mumps.py", line 17, in <module> from . import _mumps ImportError: […]/lib/python2.7/site-packages/kwant-1.1.1-py2.7-linux-x86_64.egg/kwant/linalg/_mumps.so: undefined symbol: scotchfdgraphcorderinit_ Any idea how to solve this problem? Thanks in advance! Regards, Stefan

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Re: [Kwant] install mac os (Michael Wimmer)
by Alberto Verga 27 Oct '15

27 Oct '15

Helo, I use python 2.7 and pip from homebrew: pip 7.1.2 from /usr/local/lib/python2.7/site-packages (python 2.7) I also verified that installing from the source gives the same error. However, simply putting export CFLAGS=-I/usr/local/lib/python2.7/site-packages/numpy/core/include/ solves the problem: "python setup.py build" runs smoothly. Kind regards, Alberto

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install mac os
by Alberto Verga 27 Oct '15

27 Oct '15

Hi! I installed kwant 1.0.3 on mac os with pip install kwant Since this version, the new ones point to /usr/... instead /usr/local/... to find numpy libraries: kwant/_system.c:255:10: fatal error: 'numpy/arrayobject.h' file not found #include "numpy/arrayobject.h" and the installation fails. The correct path is of the form: /usr/local/lib/python2.7/site-packages/numpy/core/include/numpy/ etc. Best wishes, Alberto Verga <mailto:Alberto.Verga@univ-amu.fr> Université d'Aix-Marseille Campus St Jérôme, service 142 13397 Marseille cedex 20, France

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Please suggest documentation to learn theory needed for Kwant..
by siddheshwar chopra 26 Oct '15

26 Oct '15

Dear All, I request you all to suggest some EASY-TO-START material/theory for understanding the concepts behind Kwant. I need to learn the basics before starting Kwant. I would be glad if you could provide any ppts. I want to feel theoretically confident before starting Kwant. Regards, -- *Dr. Siddheshwar chopra,* *M.Sc., Ph.D (Physics)Assistant Professor (Physics),* *Amity University, Noida, India.*

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quantum well
by kamal ghosh 26 Oct '15

26 Oct '15

Dear all, It has reference to 2.3.2 of "More interesting systems :Kwant 1.0.3 documentation". I have some confusions and/or misconceptions in the code of that quantum well study. These are as under: (i) in segment "# potential profile" does the scattering region mean one dimensional? I have the idea that the scattering region is two dimensional free and one dimensional bound and for size effect in this dimension several channels evolve. Scattering therefore happens from channel(s) in one lead to channel(s) in other lead with due attention to the quantized bound levels. I fail to extract this underlying physics in this part of the program. (ii) in segment "def onsite(site,pot=0):" are the onsite Hamiltonians given to the lattice sites of two dimensional region? I am misunderstood and at a loss. I want to be clear and specific which dimension is restricted to evolve the bound states? and which the other two free making a real quantum well. Once I understand that I may manipulate the number of channels and number of bound states to modify the transport. Also, if I am not wrong, the ballistic transport should be considered in the leads only; then it is the lead only where dimensionality should be considered! but I do not find this method in the lead. May be I am wrong! still then I await your wise answer to my confusions. Thanks. K.K.Ghosh mail: kk_ghosh(a)rediffmail.com

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