Kwant-discuss May 2017

kwant-discuss@python.org

12 participants
13 discussions

by ZHANG Bing

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

4 months, 2 weeks

lead_info

by Prof. CHAN Kwok Sum

Dear Kwant developer, Thank you for your effort in developing Kwant. I have a question about the definition of the direction of momentum in the smatrix.lead_info. Assume a lead lies along the y direction with primitive vector (0,1). The symmetry operation of a lead is (0,1) if the lead goes towards the positive direction and is (0,-1) if the lead goes towards the negative direction. For the momenta contained in smatrix.lead_info for these two leads , do they use the same coordinate system? Positive momenta mean the direction (0,1), negative momenta mean the direction (0,-1). For velocity, in smatrix.lead_info, it has nothing to do with the coordinate system. Positive means outgoing, negative means incoming in the lead. Thank you KS Chan Disclaimer: This email (including any attachments) is for the use of the intended recipient only and may contain confidential information and/or copyright material. If you are not the intended recipient, please notify the sender immediately and delete this email and all copies from your system. Any unauthorized use, disclosure, reproduction, copying, distribution, or other form of unauthorized dissemination of the contents is expressly prohibited.

4 years, 4 months

reproducing simple analytical solution (chain of atoms)

by Jambulat Basaev

Dear Kwant Community, In my research work I've come to the simple test problem which can be solved both using Kwant and analytically. It's about scattering of the electron wave in the chain of atoms in which hopping integral is t1 for x < 0 and t2 for x > 0. Almost all the solution is in the picture in the attachments. Realization of this analytical solution is presented in testChain.py which plots the dependence on scattering energy of the transmission coefficient |tau|**2 * v2/v1, vj = -2*tj*sin(phi_j) - velocity of the electron. The testChain-kwant.py also plots transmission coefficient versus energy in the same system, but the results are not coincide. So, my question, is it possible to reach the accordance between the solutions in both cases? P.S. Analytical solution seems to be correct, at least |rho|**2 + |tau|**2 * v2/v1 is 1 identically. P.P.S. Is it possible to draw the different hopping kinds with different colors and line styles? It can be useful for controlling errors when building the geometries with hoppings between second-neighbors... Sincerely, Jambulat

4 years, 8 months

Re: [Kwant] kwant.builder.BuilderLead

by Татьяна Матусевич

Yes, this problem is still relevant. T hank you for your help -- Tatsiana Matusevich

4 years, 8 months

Re: [Kwant] kwant.builder.BuilderLead

by Татьяна Григоренко

As a lead I want to use the left boundary atoms of graphene (please see attached photo). I use class kwant.builder.BuilderLead(builder, interface). I define a builder in the following way: #The tight-binding system of a left lead. left_lead = kwant.Builder() left_lead[lat(- 90.26501 , 13.2107 )] = 1.5 left_lead[lat(- 91.60269 , 12.67463 )] = 1.5 left_lead[lat(- 91.59045 , 11.58774 )] = 1.5 left_lead[lat(- 90.26237 , 11.08828 )] = 1.5 etc. And add hoppings left_lead[lat(- 91.60269 , 12.67463 ) , lat(- 90.26501 , 13.2107 )] = 2j left_lead[lat(- 91.59045 , 11.58774 ) , lat(- 91.60269 , 12.67463 )] = 2j left_lead[lat(- 90.26237 , 11.08828 ) , lat(- 91.59045 , 11.58774 )] = 2j left_lead[lat(- 90.26083 , 10.04835 ) , lat(- 90.26237 , 11.08828 )] = 2j etc The same way I define the interface (which called left_sequence) but without the hoppings. left_sequence = kwant.Builder() left_sequence[lat(- 88.99753 , 12.6423 )] = 1.5 left_sequence[lat(- 89.0014 , 11.61135 )] = 1.5 left_sequence[lat(- 88.9998 , 9.535691 )] = 1.5 left_sequence[lat(- 89.00571 , 8.504004 )] = 1.5 left_sequence[lat(- 88.99628 , 6.424798 )] = 1.5 etc l_lead = kwant.builder.BuilderLead(left_lead , left_sequence) sys .leads.append(l_lead) kwant.plot(sys) While I try to plot sys I have encountered an error: IndexError: Index 0 out of range (-0 <= index < 0) in dimension 0. I think that this error may appear because I incorrectly pass parameters builder and interface to a class. С уважением, Татьяна Григоренко

4 years, 8 months

performance of mumps solver and sparse solver.

by Prof. CHAN Kwok Sum

Dear Kwant Develop I have compared the performance of default, mumps solvers in windows and Ubuntu machines. Their performance is very similar without significant gain when using mumps. Do I miss anything in the installation? For example, not installing the mumps. Similar performance is found for the sparse solver. The system I considered has 10^5 to 6X10^5 sites and machine has a quad core i7 cpu with 16G RAM. My installation procedures are those found in the website for pre complled packages. KS Disclaimer: This email (including any attachments) is for the use of the intended recipient only and may contain confidential information and/or copyright material. If you are not the intended recipient, please notify the sender immediately and delete this email and all copies from your system. Any unauthorized use, disclosure, reproduction, copying, distribution, or other form of unauthorized dissemination of the contents is expressly prohibited.

4 years, 8 months

Problems with tinyarray

by Camilla Espedal

Hi again, I had to reinstall Kwant 1.3 and Tinyarray, but I get the following error message when I try to run a script using conservation_laws (script is included at the end): /usr/local/lib/python3.5/dist-packages/matplotlib-2.0.2+4130.g8ae0dbf-py3.5-linux-x86_64.egg/matplotlib/backends/backend_gtk3agg.py:18: UserWarning: The Gtk3Agg backend is known to not work on Python 3.x with pycairo. Try installing cairocffi. "The Gtk3Agg backend is known to not work on Python 3.x with pycairo. " Traceback (most recent call last): File "/home/camilla/spinHall/Kwant/Tests/spin_kwant13.py", line 45, in <module> syst = make_system(t=1.0, W=10, L=10) File "/home/camilla/spinHall/Kwant/Tests/spin_kwant13.py", line 37, in make_system syst.attach_lead(lead) File "/home/camilla/.local/lib/python3.5/site-packages/kwant/builder.py", line 1402, in attach_lead self.leads.append(BuilderLead(lead_builder, tuple(interface))) File "/home/camilla/.local/lib/python3.5/site-packages/kwant/builder.py", line 566, in __init__ self.interface = tuple(sorted(interface)) TypeError: unorderable types: tinyarray.ndarray_int() < tinyarray.ndarray_int() I used pip to install both kwant and tinyarray, using the commands in the notebook here: http://nbviewer.jupyter.org/url/antonakhmerov.org/misc/spin_conductance.ipy… The versions that pip tells me I have is: Name: kwant Version: 1.3.0a0.dev123+g3961899 Summary: Package for numerical quantum transport calculations (Python 3 version) Home-page: http://kwant-project.org/ Author: C. W. Groth (CEA), M. Wimmer, A. R. Akhmerov, X. Waintal (CEA), and others Author-email: authors(a)kwant-project.org License: BSD Location: /home/camilla/.local/lib/python3.5/site-packages Requires: numpy, scipy, tinyarray Name: tinyarray Version: 1.2.0 Summary: Arrays of numbers for Python, optimized for small sizes Home-page: https://gitlab.kwant-project.org/kwant/tinyarray Author: Christoph Groth (CEA) and others Author-email: christoph.groth(a)cea.fr License: Simplified BSD license Location: /usr/local/lib/python3.5/dist-packages Requires: I got into a similar problem earlier, but then it was because I had the wrong version of tinyarray (not dev), but now I think I have installed it correctly. Can you help me? Best, Camilla

4 years, 8 months

Kwant 1.3 has been released

by Christoph Groth

After more than one year of development, we are extremely pleased to announce the release of Kwant 1.3. Kwant 1.3 supports * discretizing of continuum Hamiltonians, * calculating and displaying local densities and currents, * declaring and using symmetries and conservation laws, * calculating bulk properties using the kernel polynomial method, * finalizing builders with multiple translational symmetries, and has many other improvements that are detailed in the "what's new in Kwant 1.3" document [1]. The installation instructions [2] have been updated to explain how to install Kwant 1.3 on computers running GNU/Linux, Mac OS, and Windows. Note that thanks to the package manager Conda it is now much easier to install Kwant under Mac OS and on Unix accounts without root privileges. The new version is practically 100% backwards-compatible with scripts written for previous versions of Kwant 1.x. The Kwant team is happy to welcome Joseph Weston as a member. We are also grateful to the many contributors without whom this release would not be nearly as good: * Jörg Behrmann * Bas Nijholt * Michał Nowak * Viacheslav Ostroukh * Pablo Pérez Piskunow * Tómas Örn Rosdahl * Sebastian Rubbert * Rafał Skolasiński * Adrien Sorgniard We would like to hear your feedback at kwant-discuss(a)kwant-project.org. [1] https://kwant-project.org/doc/1.3/pre/whatsnew/1.3 [2] https://kwant-project.org/install

4 years, 8 months

Problems with Kwant 1.3 and tinyarray

by Camilla Espedal

Hi again, I had to re-install Kwant 1.3 and tinyarray (dev-version) because of some problems with pip and matplotlib. Anyhow, I can't seem to get it to work, I get the same error that I got earlier when I had installed the wrong version of tinyarray, namely: /usr/local/lib/python3.5/dist-packages/matplotlib-2.0.2+4130.g8ae0dbf-py3.5-linux-x86_64.egg/matplotlib/backends/backend_gtk3agg.py:18: UserWarning: The Gtk3Agg backend is known to not work on Python 3.x with pycairo. Try installing cairocffi. "The Gtk3Agg backend is known to not work on Python 3.x with pycairo. " Traceback (most recent call last): File "/home/camilla/spinHall/Kwant/Tests/spin_kwant13.py", line 45, in <module> syst = make_system(t=1.0, W=10, L=10) File "/home/camilla/spinHall/Kwant/Tests/spin_kwant13.py", line 37, in make_system syst.attach_lead(lead) File "/home/camilla/.local/lib/python3.5/site-packages/kwant/builder.py", line 1402, in attach_lead self.leads.append(BuilderLead(lead_builder, tuple(interface))) File "/home/camilla/.local/lib/python3.5/site-packages/kwant/builder.py", line 566, in __init__ self.interface = tuple(sorted(interface)) TypeError: unorderable types: tinyarray.ndarray_int() < tinyarray.ndarray_int() I run pip show kwant, and pip show tinyarray, and get

4 years, 8 months

use of a function to define the on-site energy in the leads

by Sebastiano Peotta

Dear developers of Kwant, I have seen most of the examples of Kwant usage, but somehow I miss the usage of functions to define the on-site energy of lattice sites in the leads. I have attached a simple Kwant script which includes the following lines ----------------- sym = kwant.TranslationalSymmetry((0, -1.)) lead = kwant.Builder(sym) lead[lat.shape(region_lead,(0.,0.))] = 4. + potential # use the same potential also for the lead !!! lead[lat.neighbors()] = -1. ------------------ the crucial line is the third one, where the function "potential" that defines the potential in the scattering region is used also in the lead. Since the leads are automatically attached to the scattering region I would expect that the potential is evaluated at the sites where the leads is attached and then repeated according to the translational symmetry given to the lead. Is this the case? I tried to check this using the "map" method in kwant.plotter, but the color in correspondence of the leads is an uninformative grey, which does not belong to the color scale used in the scattering region. Somehow in the documentation I was not able to find what happens when a function is used to define the onsite energy in a lead. Can you fill this gap? Thanks for your help in advance, Sebastiano

4 years, 8 months

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Kwant-discuss May 2017