```python
from pyscf import gto, scf, dft
from pyscf.pbc import gto as pbcgto, scf as pbcscf, dft as pbcdft
from pyscf.pbc.tools import pywannier90
import numpy as np
import matplotlib.pyplot as plt
import mcu

# Define the unit cell
cell = pbcgto.Cell()
cell.atom = '''
He 0 0 0
He 1 0 0
He 0 1 0
He 0 0 1
'''
cell.a = np.eye(3) * 4.0
cell.basis = 'gth-dzvp'
cell.pseudo = 'gth-pade'
cell.verbose = 4
cell.build()

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

# Save and load the kks object
mf.to_chkfile('pbe.chk')
kks = pbcdft.KRKS.from_chk('pbe.chk')

# Construct MLWFs
w90 = pywannier90.Wannier90(kks, num_wann=4, dis_num_iter=5000)
w90.kernel()

# Export the MLWFs in xsf format for plotting
w90.plot_wf(grid=[10, 10, 10], supercell=[2, 2, 2], fname='mlwf.xsf')

# Export certain matrices and run a wannier90 using these
w90.export_unk(grid=[10, 10, 10])
w90.export_centers_scf()
w90.export_lattice()
w90.export_hamiltonian()

# Interpolate the Fock or band structure using the Slater-Koster scheme
band_kpts, band_energies = w90.interpolate_band(grid=[10, 10, 10])

# Perform SCF calculation to get the band structure
kpts_band = cell.make_kpts(band_kpts)
mf_band = pbcdft.KRKS(cell, kpts=kpts_band)
mf_band.xc = 'pbe'
mf_band.kernel()
scf_bands = mf_band.mo_energy

# Print the difference in the eigenvalues interpolated by scf.get_bands function and by pywannier90
print("Difference in eigenvalues:", np.abs(band_energies - scf_bands).mean())

# Plot the band structure using mcu
fig, ax = plt.subplots()
kpath = np.arange(len(band_kpts))
for i in range(band_energies.shape[1]):
    ax.plot(kpath, band_energies[:, i], color='b', label='Wannier90' if i == 0 else "")
    ax.plot(kpath, scf_bands[:, i], '--', color='r', label='SCF' if i == 0 else "")
ax.set_xlabel('k-point')
ax.set_ylabel('Energy (eV)')
ax.legend()
plt.show()
```