human
I am working on the file "A_03/run.ipynb".
The first task is:
2. Construct Hamiltonian and add magnetic fields
The required field strengths may vary depending on the size of the hall bar.
A good starting point might by B = 1 / np.arange(1,31)
Can you write Python program for it?

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Write me a the Python program you requested?
assistant
#Here is the Python program you requested.

def peierls(B=0):
    def peierls(self, ia, atoms, atoms_xyz=None):
        idx = self.geometry.close(ia, R=[0.1, 1.01], atoms=atoms, atoms_xyz=atoms_xyz)
        # Onsite
        self[ia, idx[0]] = 4
    
        # Hopping
        if B == 0:
            self[ia, idx[1]] = -1
        else:
            xyz = self.geometry.xyz[ia]
            dxyz = self.geometry[idx[1]]
            self[ia, idx[1]] = - np.exp(-0.5j * B * (dxyz[:, 0] - xyz[0])*(dxyz[:,1] + xyz[1]))
    return peierls

# H0 = sisl.Hamiltonian(geom, dtype=np.float64)
# H0.construct(peierls()))
#
# HB = sisl.Hamiltonian(geom, dtype=np.complex128)
# HB.construct(peierls(B))
# 
# dH = ...