Mailman 3 November 2023 - Kwant-discuss

To to separate spins, electron and hole
by Khani Hosein 11 Oct '24

11 Oct '24

Dear all, I am using Kwant to study a system with both spins and electron and hole, so the hopping matrix is 4X4. Now I want to know how to separate the spins, electron and hole. I study this through the "2.6. Superconductors: orbital degrees of freedom, conservation laws and symmetries" smatrix = kwant.smatrix(syst, energy) data.append(smatrix.submatrix((0, 0), (0, 0)).shape[0] -smatrix.transmission((0, 0), (0, 0)) +smatrix.transmission((0, 1), (0, 0))) I do not find more information about this for kwant. For my system, if I have 3 leads, and the hopping and onsite energy is set in this order: (e↑,0,0,0)- spin up electron,first row of the 4X4matrix (0,e↓,0,0)- spin down electron,second row of the 4X4matrix (0,0, h↑ ,0)- spin up hole,third row of the 4X4matrix (0,0, 0, h ↓ )- spin down hole,fourth row of the 4X4matrix I want to obtain the transmissions from 0 →2. smatrix = kwant.smatrix(syst, energy) The transmission from h↑ to e↑ is: smatrix.transmission((2, 1), (0, 2)) The transmission from h ↓ to e↑ is: smatrix.transmission((2, 1), (0, 3)) Is my understanding correct? Thanks very much in advance! Hosein Khani

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[kwant] Introducing KPM Tools: Advanced KPM Expansions for Kwant
by pablo.perez.piskunow＠gmail.com 23 Dec '23

23 Dec '23

Dear Kwant Community, I'm pleased to announce the release of "KPM Tools," an open-source Python package specifically designed to extend the Kernel Polynomial Method (KPM) functionalities within Kwant, focusing on closed tight-binding systems. ## Acknowledgment to Kwant: KPM Tools builds upon the solid foundation of Kwant. The package aims to complement and enhance Kwant's existing KPM features, adhering to the high-quality standards established by the Kwant project. See the original KPM implementation in Kwant: https://kwant-project.org/doc/1/tutorial/kpm https://kwant-project.org/doc/1/reference/kwant.kpm ## About KPM Tools: KPM Tools expands the KPM capabilities in Kwant, offering advanced expansions of spectral functions like Density of States, Green's Functions, Kubo Conductivity, and Chern Markers. We introduce enhanced tools systems with periodic boundaries, including new KPM vector factories and adapted velocity and distance operators. Last but not least, I include an extremely efficient time evolution operator expansion. All the features are exemplified in the tutorials: https://kpm-tools.readthedocs.io/en/latest/tutorials.html KPM Tools is available for installation via pip: `` $ pip install kpm-tools ``` You can find more details in the `kpm-tools` repository: https://github.com/piskunow/kpm-tools and the documentation: https://kpm-tools.readthedocs.io https://kpm-tools.readthedocs.io/en/latest/api.html ## Contributions Welcome: I invite contributions, particularly in improving documentation and the 'concatenator' function/module. The documentation consists mainly of Jupyter Notebooks, allowing for easy local testing and updates. As my time to dedicate to further development is limited, your contributions, whether in code, documentation, or ideas, are not just welcome but crucial for the growth of KPM Tools. Pull requests and collaborative efforts will significantly enhance the utility and reach of this package. Looking forward to your insights, feedback, active participation in improving KPM Tools, and seeing how KPM Tools can contribute to your research and projects. Best regards, Pablo Piskunow

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Conda distribution -- how do you find the libraries kwant is linked to?
by poatajoseph＠gmail.com 07 Dec '23

07 Dec '23

Hi all, After looking through old threads I came across [1], which discusses the effect LAPACK-level parallelization has on preformance. For the user that started that thread, they saw improvements by changing their environmental variables. This I understand, what is confusing me is how you figure out which library a Kwant distribution is linked to. E.g. without setting these independently and observing what effect each has on performance, how can I tell which of the following environmental variables need to be changed? OPENBLAS_NUM_THREADS OMP_NUM_THREADS MKL_DYNAMIC MKL_NUM_THREADS I used conda to install Kwant on my M1 Macbook air. Where should I be looking in the root directory of my Kwant distribution for this information? Or is there another way to check this? Thanks, Joe

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Plotting Andreev Bound State Spectrum (as a function of phase bias) in S-N-S Josephson Junction
by sc20rs001＠iiserkol.ac.in 22 Nov '23

22 Nov '23

Hi All! Can anyone help me with how to plot the Andreev bound state spectrum (as a function of phase bias) for an S-N-S Josephson junction? Thanks in advance.

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Plotting band structure (spaghetti diagram) from 2d band structure
by Lucas McBee 14 Nov '23

14 Nov '23

Hello, Is there any way to plot a band structure projection, colloquially known as spaghetti diagrams, from a 2d system with symmetry from wraparound.wraparound. ? I know how to use wraparound.plot_2d_bands, but this is a three dimensional plot that is hard to read. Best, LM

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Could Kwant deal with non-orthogonal tight-binding bases
by 45777601＠qq.com 13 Nov '23

13 Nov '23

Colud Kwant solvers currently support overlap matrices? It was not supported three years ago. It is not clear whether this feature is added now. https://gitlab.kwant-project.org/kwant/kwant/-/issues/370

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Package announcement: Pymablock
by Anton Akhmerov 12 Nov '23

12 Nov '23

Hello fellow Kwanters, I am happy to announce Pymablock, a Python package useful to combine with Kwant. Its main purpose is constructing effective models using perturbation theory, which may help you in different ways. Pymablock allows you to analyse the behavior of a few levels of a large Hamiltonian, or to construct a symbolic k.p model. We originally wrote the code for one of our projects, but then saw that this tool is useful almost for the entire group, so we decided to turn it into a package. We spent countless hours generalizing, optimizing, and testing it so that it is efficient and reliable. Now it handles multiple perturbations to any order, and it is compatible with symbolic and numerical calculations. We hope that Pymablock will save you a lot of effort and computation time. To see where it can help, check out our its documentation (https://pymablock.rtfd.io/), and in particular the tutorials about the k.p model of bilayer graphene (https://pymablock.readthedocs.io/en/latest/tutorial/bilayer_graphene.html) or the induced superconducting gap (https://pymablock.readthedocs.io/en/latest/tutorial/induced_gap.html). Just like Kwant, Pymablock is open source (https://gitlab.kwant-project.org/qt/pymablock), and you are welcome to follow and contribute to its development. Let us know if you have any questions or comments! Also if there's interest we can organize an online introduction of the package Best, Anton Akhmerov and the Pymablock maintainers: Isidora Araya Day and Sebastian Miles

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How to introduce buckling in monolayer buckled Xenes like silicene, germanene, stanene etc.
by Swastik Sahoo 03 Nov '23

03 Nov '23

Hello, I want to introduce buckling term to the lattice structure of buckled monolayer Xenes like silicene, germanene, stanene etc. to differentiate them from planar graphene. Will the lattice structure be able to show the buckling ? Thanks and Regards, Swastik Sahoo. Research Scholar, EE Dept. IIT Bombay. Ph. No- 9980387383 mail id:- swastik.sahoo79(a)gmail.com swastik(a)ee.iitb.ac.in

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