Dear Sayan Mondal,
I would suspect that the values for which you are seeing these errors are those that are close to a topological phase transition. In these cases, the hybrid Wannier charge center evolution changes more abruptly, and the calculation would take longer to converge.
To increase the number of steps the calculation will perform before aborting, you can decrease the 'min_neighour_dist' value, and increase the upper limit of the 'iterator' (these keywords are described in the surface.run reference https://z2pack.greschd.ch/en/latest/reference/surface.html#z2pack.surface.run).
For values of lambda_R and lambda_v which are exactly at a phase transition, the calculation will not converge, because the topological indices are not well-defined.
Best regards,
Dominik Gresch
On 17.09.21 08:28, SAYAN MONDAL wrote:
Dear Developer, I am trying to get the phase diagram of the Kane-Mele model as described in Fig. 1 of (https://doi.org/10.1103/PhysRevLett.95.146802 https://doi.org/10.1103/PhysRevLett.95.146802). The Z2 invariant is 1 inside the curve while it vanishes outside. So I tried to get the Z2 invariant for several values of lambda_R and lambda_v. The code is giving correct results for some values of lambda_R and lambda_v, but for some other values it is showing some errors as follows:
WARNING: Iterator stopped before the calculation could converge. WARNING: Iterator stopped before the calculation could converge. WARNING: 'min_neighbour_dist' reached: cannot add line at t = 0.6562500000000001 WARNING: Iterator stopped before the calculation could converge. WARNING: Iterator stopped before the calculation could converge. WARNING: 'min_neighbour_dist' reached: cannot add line at t = 0.6562500000000001 WARNING: Iterator stopped before the calculation could converge. WARNING: Iterator stopped before the calculation could converge. WARNING: 'min_neighbour_dist' reached: cannot add line at t = 0.6562500000000001
My code is attached below:
import logging
import z2pack import numpy as np from numpy import cos, sin, kron, sqrt import matplotlib.pyplot as plt
logging.getLogger('z2pack').setLevel(logging.WARNING)
# defining pauli matrices identity = np.identity(2, dtype=complex) pauli_x = np.array([[0, 1], [1, 0]], dtype=complex) pauli_y = np.array([[0, -1j], [1j, 0]], dtype=complex) pauli_z = np.array([[1, 0], [0, -1]], dtype=complex)
def get_kane_mele_hamiltonian(t, lambda_v, lambda_R, lambda_SO): def inner(k): k = np.array(k) * 2 * np.pi kx, ky = k # change to reduced coordinates x = (kx - ky) / 2 y = (kx + ky) / 2 return ( t * (1 + 2 * cos(x) * cos(y)) * kron(pauli_x, identity) + lambda_v * kron(pauli_z, identity) + lambda_R * (1 - cos(x) * cos(y)) * kron(pauli_y, pauli_x) + -sqrt(3) * lambda_R * sin(x) * sin(y) * kron(pauli_y, pauli_y) + 2 * t * cos(x) * sin(y) * kron(pauli_y, identity) + lambda_SO * (2 * sin(2 * x) - 4 * sin(x) * cos(y)) * kron(pauli_z, pauli_z) + lambda_R * cos(x) * sin(y) * kron(pauli_x, pauli_x) + -sqrt(3) * lambda_R * sin(x) * cos(y) * kron(pauli_x, pauli_y) )
return inner
if __name__ == '__main__': arr = [] lambda_R_list = np.linspace(0, 0.31, 20) lambda_v_list = np.linspace(0, 0.24, 20) for lR in lambda_R_list: for lv in lambda_v_list: system = z2pack.hm.System( get_kane_mele_hamiltonian( t=1, lambda_v = lv, lambda_R=lR, lambda_SO=0.06 ), dim=2, check_periodic=True ) res = z2pack.surface.run(system=system, surface=lambda s, t: [s / 2, t]) # print('Z2 invariant: {}'.format(z2pack.invariant.z2(res))) val = z2pack.invariant.z2(res) arr.append([lR, lv, val]) arr = np.asarray(arr) np.savetxt('pd.txt', arr) print(arr) # z2pack.plot.wcc(res, axis=ax) # ax.set_xticks([0, 1]) # ax.set_xticklabels(['0', '0.5']) # ax.set_xlabel(r'$k_y$') # ax.set_yticks([0, 1]) # ax.set_ylabel(r'$\bar{y}$', rotation='horizontal') # plt.savefig('plot.pdf', bbox_inches='tight')
Is there any way to correct those errors? I shall look forward to your kind cooperation.
Thank you
Best Regards, Sayan Mondal, Research Scholar, Dept. of Physics, Roll No. - 186121022, E-mail: mondal18@iitg.ac.in Indian Institute of Technology Guwahati Guwahati - 781039