Z2 invariant from evolution of Wannier charge centers

wannier_charge_bi111.py

from tightbinder.models import SlaterKoster
from tightbinder.fileparse import parse_config_file
from tightbinder.topology import calculate_wannier_centre_flow, plot_wannier_centre_flow, calculate_z2_invariant
import matplotlib.pyplot as plt
from pathlib import Path

def main():

    # Parse configuration file
    path = Path(__file__).parent / ".." / "examples" / "inputs" / "Bi111.yaml"
    config = parse_config_file(path)

    # Init. model and Hamiltonian
    model = SlaterKoster(config)
    model.initialize_hamiltonian()

    # Compute Wannier charge centre evolution
    nk = 20
    wcc = calculate_wannier_centre_flow(model, nk, refine_mesh=False)

    # Plot evolution of the charge centers and compute the Z2 invariant
    plot_wannier_centre_flow(wcc)
    print(f"Z2 invariant: {calculate_z2_invariant(wcc)}")


if __name__ == "__main__":
    main()
    plt.show()

This code should produce the following plot:

And the following output:

Z2 invariant: 1