Mailman 3 June 2024 - 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 … [View More]

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Unexpected Landau Level Discrepancies in Multilayer Graphene Compared to Published Results
by yl June 22, 2024

June 22, 2024

Dear Kwant Group, I attempted to replicate the Landau levels of ABA-trilayer graphene as described in the paper "Landau level spectra and the quantum Hall effect of multilayer graphene," Physical Review B 83, 165443 (2011), Figure 2, using Kwant. The results obtained with Kwant match the paper's results approximately well; however, there is an issue. The number of Landau levels (LLs) under each magnetic field does not match the results presented in the paper. For example (see the attached … [View More]

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[kwant] How to make a finite lead?
by 김봉수 June 12, 2024

June 12, 2024

Dear kwant users, I am trying to reproduce the paper following. https://arxiv.org/abs/1110.4280 (in this paper, fig5, 6 will help to understand my questions.) What I’m struggling with now is to build a finite(not infinite, and not having any translational symmetry) lead as below. I wonder 1. I think "kwant.builder.SelfEnergyLead()” function might be proper thing to build a finite lead without any translational symmetry. Is it correct? 2. If it's right, when I run this code using … [View More]

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Error in calculating conductance of 3D system with periodic boundaries
by Naveen Yadav June 7, 2024

June 7, 2024

Dear Kwant Developers, I am trying to calculate the conductance of a 3D system with dimension L × W × H, by imposing periodic boundary conditions in all three directions. I am able to calculate the band structure but unable to calculate the corresponding conductance using kwant.smatrix. I am not sure whether kwant is able to do transport calculations on systems with periodic boundaries using smatrix. Please advise. The code is following import kwant import scipy.sparse.linalg as sla import … [View More]matplotlib.pyplot as plt import tinyarray import numpy as np from numpy import cos, sin, pi import cmath from cmath import exp from matplotlib import rc, rcParams rc('text', usetex=True) rc('axes', linewidth=2) rc('font', weight='bold') #rcParams['text.latex.preamble'] = [r'\usepackage{sfmath} \boldmath'] #rcParams['text.latex.preamble'] = [r'\usepackage{sfmath} \boldmath'] 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]]) def make_sys(a=1, m_0 = 2, L=1, W=100, H=1, t=1.0, t_z=0.0, phi=0.01): #L=10; W=80; H=60; def onsite(site): return 2 * m_0 * sigma_x def hoppingx(site0, site1): y = site1.pos[1] return (t * sigma_x) def hoppingy(site0, site1): return -1j * t * sigma_y - (m_0/2) * sigma_x def hoppingz(site0, site1): y = site1.pos[1] return (-1j * t * sigma_z - (m_0/2) * sigma_x - 1j * t_z * sigma_0) * exp(2 * pi * 1j * (y) * phi) lat =kwant.lattice.cubic(norbs=2) #sys = kwant.Builder(kwant.TranslationalSymmetry(lat.vec((0, 0, H)))) #sys[(lat(x, y, z) for x in range(L) for y in range(W) for z in range(H))] = onsite #sys = kwant.Builder(kwant.TranslationalSymmetry((L, 0, 0),(0, 0, H))) #sys[(lat(0, y, 0) for y in range(W))] = onsite sys = kwant.Builder(kwant.TranslationalSymmetry((L, 0, 0),(0, W, 0),(0, 0, H))) sys[lat.shape(lambda p: True, (0,0,0))] = onsite sys[kwant.builder.HoppingKind((1, 0, 0), lat, lat)] = hoppingx sys[kwant.builder.HoppingKind((0, 1, 0), lat, lat)] = hoppingy sys[kwant.builder.HoppingKind((0, 0, 1), lat, lat)] = hoppingz sys = kwant.wraparound.wraparound(sys, keep=None) leadL = kwant.Builder(kwant.TranslationalSymmetry((-a, 0, 0),lat.vec((0, W, 0)),lat.vec((0, 0, H)))) leadL[(lat(0, y, z) for y in range(W) for z in range(H))] = onsite leadL[kwant.builder.HoppingKind((1, 0, 0), lat, lat)] = hoppingx leadL[kwant.builder.HoppingKind((0, 1, 0), lat, lat)] = hoppingy leadL[kwant.builder.HoppingKind((0, 0, 1), lat, lat)] = hoppingz leadR = kwant.Builder(kwant.TranslationalSymmetry((a, 0, 0),lat.vec((0, W, 0)),lat.vec((0, 0, H)))) leadR[(lat(0, y, z) for y in range(W) for z in range(H))] = onsite leadR[kwant.builder.HoppingKind((1, 0, 0), lat, lat)] = hoppingx leadR[kwant.builder.HoppingKind((0, 1, 0), lat, lat)] = hoppingy leadR[kwant.builder.HoppingKind((0, 0, 1), lat, lat)] = hoppingz leadL = kwant.wraparound.wraparound(leadL, keep=0) leadR = kwant.wraparound.wraparound(leadR, keep=0) sys.attach_lead(leadL) sys.attach_lead(leadR) sys = sys.finalized() return sys syst=make_sys() def plot_bands_2d(syst, momenta=(101, 101, 101), ky=0, kz=0): if not isinstance(syst, kwant.system.FiniteSystem): raise TypeError("Need a system without symmetries.") fig = plt.figure(figsize=(5, 5)) #kwant.plotter.bands(syst.leads[0], momenta=np.linspace(-np.pi, np.pi, 101), show=False) kxs = np.linspace(-np.pi, np.pi, momenta[0]) def get_energies(ky=ky, kz=kz): energies = [np.linalg.eigvalsh(syst.hamiltonian_submatrix ((kx, ky, kz))) for kx in kxs] return energies energies = np.array(get_energies(ky=ky, kz=kz)) # Plot the band structure for band in np.array(energies).T: plt.plot(kxs, band) plt.ylim(-2.5, 2.5) plt.xlim(-pi, pi) plt.xlabel("kx") plt.ylabel("Energy") plot_bands_2d(syst) kzs = np.linspace(-pi,pi,101) kys = np.linspace(-pi,pi,101) energies = np.linspace(0.0, 0.5, 30) data=[] for energy in energies: Tkx = np.zeros(101) for i in np.arange(len(kzs)): kz=kzs[i] ky=kys[i] smatrix = kwant.smatrix(syst, energy, [kz], [ky]) Tkx[i]=smatrix.transmission(1, 0) data.append(sum(Tkx)) plt.plot(energies, data) plt.show() Also as a separate question, I am trying to run the notebook Kubo_Bastin_conductivity_with_periodic_boundary_conditions.ipynb from https://gitlab.com/kpm-tools/bloch/-/tree/master/examples?ref_type=heads to understand the kubo conductivity calcualton on a system with periodic boundaries but various errors are there in importing bloch.py. I am using kwant.__version__ = '1.4.4'. Please help in this regard. Thanks in advance. -- Best Regards, Naveen Yadav Department of Physics & Astrophysics University Of Delhi New Delhi-110007 [View Less]

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ValueError: Value functions must not take *args or **kwargs
by wilson2048＠outlook.com June 4, 2024

June 4, 2024

Dear kwant community: I have encountered this error in my code. Basically I don't want to redefine the hop in the y direction, so I use the existing function `hop`. However, the code throw me an error which I don't know how to fix. Below is a simplest code example, the real situation is more complex but the spirit is the same. ``` lat = kwant.lattice.square() def make_system(r=10, t=1): def circle(pos): x, y = pos return x**2+y**2<r**2 syst = kwant.Builder() … [View More]

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Leads self-energy matrix elements not ordered as system's hamiltonian_submatrix?
by wilson2048＠outlook.com June 4, 2024

June 4, 2024

Dear kwant community: I am investigating the `kwant.greens_function`。 I would like to get the lead self-energies and add to the original system Hamiltonian and then inverse it, thus obtaining the retarded green's function. I tested, but the resulted green's function is not identical to the one kwant calculated. I want to know the reason. Is it because what I describe in the title? Below is a minimal code example: ``` lat = kwant.lattice.square() def make_system(r=20, t=-1): def circle(… [View More]

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Kwant-compatible Hartree-Fock Package
by Johanna June 3, 2024

June 3, 2024

Hi all, We're excited to share a new Python package we've developed at the Quantum Tinkerer group: MeanFi. MeanFi is a self-consistent Hartree-Fock solver for tight-binding models designed to work smoothly with Kwant. Our algorithm is optimized to easily and extensibly perform all your mean-field calculations. We made it such that you can: 1) define the initial Hamiltonian and the density-density interaction as Kwant models, 2) turn it into a tight-binding format, 3) find the groundstate … [View More]

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