```python
from pyscf import gto, scf, dft
from pyscf.pbc import gto as pgto, scf as pscf
from pyscf.pbc.tools import pywannier90
import numpy as np
import matplotlib.pyplot as plt

# Define a unit cell
cell = pgto.Cell()
cell.atom = '''
He 0. 0. 0.
He 1. 0. 0.
He 0. 1. 0.
He 0. 0. 1.
'''
cell.basis = 'gth-szv'
cell.pseudo = 'gth-pade'
cell.a = np.eye(3) * 4.
cell.build()

# Perform a PBE calculation
kpts = cell.make_kpts([2,2,2])
mf = pscf.KRKS(cell, kpts)
mf.xc = 'pbe'
mf.kernel()

# Save and load the kks object
mf.with_df._cderi_to_save = 'kks.h5'
mf.with_df.to_disk()
mf.with_df.from_disk()

# Construct MLWFs
w90 = pywannier90.W90(mf, cell, kpts)
w90.kernel()

# Export the MLWFs in xsf format for plotting
w90.export_unk()
w90.export_AME()

# Export certain matrices and run a wannier90 using these
w90.make_win()
w90.setup()
w90.export_unk()
w90.export_AME()

# Interpolate the Fock or band structure using the Slater-Koster scheme
bands_kpts, bands_wghts = w90.interpolate_band(np.linspace(0, 1, 100), cell.lattice_vectors()[:1])
fock_interpolated = w90.interpolate_fock(bands_kpts)

# Print the difference in the eigenvalues interpolated by scf.get_bands function and by pywannier90
kpts_band = cell.make_kpts(bands_kpts)
mf_kpts = pscf.KRKS(cell, kpts_band)
mf_kpts.kernel()
scf_bands = mf_kpts.get_bands(kpts_band)[0]

print("Difference in eigenvalues:", np.abs(scf_bands - fock_interpolated).max())

# Plot the band structure using mcu
plt.plot(bands_kpts[:,0], fock_interpolated, 'r-', label='Interpolated by pywannier90')
plt.plot(bands_kpts[:,0], scf_bands, 'b--', label='SCF bands')
plt.xlabel('k-path')
plt.ylabel('Energy (a.u.)')
plt.legend()
plt.show()
```