Mailman 3 August 2023 - Kwant-discuss

To to separate spins, electron and hole
by Khani Hosein Oct. 11, 2024

Oct. 11, 2024

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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Package announcement: Pymablock
by Anton Akhmerov Nov. 12, 2023

Nov. 12, 2023

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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Realistic values of hopping parameters
by Yu Li Oct. 19, 2023

Oct. 19, 2023

Dear all, Now I’m studying some transport property based on multilayered system, with nonmagnetic layer/ferromagnetic layer (NM/FM) stack. May I ask when creating a tight binding system, and setting hoppings by the following function: syst[(lat(1, 0), lat(1, 1))] = t, how to associate the hopping with a realistic system? Such as hoppings between FM and FM atoms, or between FM and NM atoms? I found in many literatures people just simply put t=1, but I assume the value should depend on the type of atoms. My another question is, is it possible to define more than one type of hopping between two sites? For the tight-binding approximation of p electrons, there are two types of hopping integrals: Vppσ, and Vppπ, so I’m wondering if it’s possible to simulate the effect of both hoppings? Thanks a lot for reading my questions! Cheers, Yu Li

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Questions about kwant: the number of iterations
by meimeiwu＠buaa.edu.cn Sept. 5, 2023

Sept. 5, 2023

Hi devs, I am learning kwant alone, but I have doubts. I have several confusions which are related to calculate transport by using kwant： 1. When disorder is included what the number of iterations or what is the convergence standard in calculation ？ 2. Will the length of scattering region affect computed result ？For example, I construct the system with scattering region and two leads, will the length of scattering region affect the transport properties? If the length of scattering region is too small, is there any interaction between two leads? If transport properties depend on the length of scattering region, what we should consider it? What calculations can illustrate the influence of the length of scattering region? what is the best solution or if you can give me some advices to solve that problem I will appreciate it, thanks a lot! Best regards

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About 'kwant.kpm.SpectralDensity'
by Gabriel Garcia Sept. 2, 2023

Sept. 2, 2023

Hi devs, I have been using the 'kwant.kpm.SpectralDensity' command to calculate the density of states (DoS) of a system. I noticed that this command calculates the DoS only around zero energie. How to calculate the DoS for higher energy levels? I tried using the 'np.linspace' command to set the energy range, but how much larger the energy range is, it's more inaccurate the DoS becomes. Does anyone know how to calculate the DoS for high energy levels? Gabriel Garcia

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Non reciprocal hopping in kwant
by Md Afsar Reja Aug. 28, 2023

Aug. 28, 2023

Dear kwant-team, Is it possible to implement non-reciprocal hopping( e.g. different magnitude in left-right hopping like the non-hermitian Hatano-Nelson model ) in the current available Kwant version? Thanks! Best regards, reja

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troubles ussing kwant and anaconda in cluster computer
by jorge huamani Aug. 9, 2023

Aug. 9, 2023

Dear kwant -Team I am getting troubles with kwant on my python environment in my cluster computers, basically after the installation of anaconda, ipyparallel and kwant, I got the following error on my ipython editor, 1.. ipython 2. import kwant illegal instruction, the same things happened when I try to run with python3 teste.py (import kwant inside) what is the best solution or if you can give me some advices to solve that problem I will appreciate it, thanks a lot Best regards -- Dr. Jorge Huamaní Correa Professor at Universidad Tecnológica del Perú CTI Vitae : https://ctivitae.concytec.gob.pe/appDirectorioCTI/VerDatosInvestigador.do?i…

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Installation Issue with tkwant - Need Assistance
by Dibyendu Kuiri Aug. 9, 2023

Aug. 9, 2023

Dear tkwant forum, I hope this email finds you well. I am writing to seek assistance regarding an issue I am facing while trying to install tkwant using conda. I am attempting to install tkwant in a conda environment named 'env-tkwant' by executing the following command: "conda install tkwant -c conda-forge". "Collecting package metadata (current_repodata.json): done Solving environment: unsuccessful initial attempt using frozen solve. Retrying with flexible solve. Solving environment: unsuccessful attempt using repodata from current_repodata.json, retrying with next repodata source." Despite my attempts, I haven't been able to resolve this issue and successfully install tkwant in the specified environment. I have already tried to install from the 'conda-forge' channel, but the problem persists. I would greatly appreciate any help or suggestions to resolve this problem. Many thanks, Dibyendu Kuiri, Academic Centre for Materials and Nanotechnology AGH University of Science and Technology. Av. Mickiewicza 30 30-059 Krakow, Poland. email: kuiri(a)agh.edu.pl Phone no: +48 881293791 www.acmin.agh.edu.pl

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