  from pyscf import gto, scf, cc

# Build the cell
cell = gto.Cell()
cell.atom = '''
C 0.000000 0.000000 0.000000
C 1.000000 1.000000 1.000000
'''
cell.basis = '6-31g'
cell.pseudo = 'gth-pade'
cell.lattice_vectors = [[3.0, 0.0, 0.0], [0.0, 3.0, 0.0], [0.0, 0.0, 3.0]]
cell.unit = 'B'
cell.build()

# Perform KHF and KCCSD calculations with 2x2x2 k-points
kpts = cell.make_kpts([2, 2, 2])
khf = scf.RHF(cell, kpts)
ehf = khf.kernel()
kccsd = cc.CCSD(cell, kpts)
eccsd = kccsd.kernel()
print('Total energy per unit cell (KHF):', ehf)
print('Total energy per unit cell (KCCSD):', eccsd)

# Perform KHF and KCCSD calculations for a single k-point
kpts = cell.make_kpts([1, 1, 1])
khf = scf.RHF(cell, kpts)
ehf = khf.kernel()
kccsd = cc.CCSD(cell, kpts)
eccsd = kccsd.kernel()
print('Total energy per unit cell (KHF):', ehf)
print('Total energy per unit cell (KCCSD):', eccsd)

# Perform a single k-point calculation using the RHF method, run RCCSD, and print the total energy per unit cell
kpts = cell.make_kpts([1, 1, 1])
rhf = scf.RHF(cell)
ehf = rhf.kernel()
rccsd = cc.RCCSD(cell)
eccsd = rccsd.kernel()
print('Total energy per unit cell (RHF):', ehf)
print('Total energy per unit cell (RCCSD):', eccsd)

# Calculate and print the RCCSD energy based on CCSD density matrices
kpts = cell.make_kpts([1, 1, 1])
rhf = scf.RHF(cell)
ehf = rhf.kernel()
rccsd = cc.RCCSD(cell)
eccsd = rccsd.kernel()
print('RCCSD energy:', eccsd)

# Convert the RHF object to a UHF object, run UCCSD, and print the total energy per unit cell at the k-point
kpts = cell.make_kpts([1, 1, 1])
rhf = scf.RHF(cell)
uhf = scf.UHF(cell)
ehf = rhf.kernel()
uccsd = cc.UCCSD(cell)
eccsd = uccsd.kernel()
print('Total energy per unit cell (UHF):', ehf)
print('Total energy per unit cell (UCCSD):', eccsd)

# Calculate and print the UCCSD energy based on CCSD density matrices
kpts = cell.make_kpts([1, 1, 1])
rhf = scf.RHF(cell)
uhf = scf.UHF(cell)
ehf = rhf.kernel()
uccsd = cc.UCCSD(cell)
eccsd = uccsd.kernel()
print('UCCSD energy:', eccsd)

# Convert the UHF object to a GHF object, run GCCSD, and print the total energy per unit cell at the k-point
kpts = cell.make_kpts([1, 1, 1])
rhf = scf.RHF(cell)
uhf = scf.UHF(cell)
ghf = scf.GHF(cell)
ehf = rhf.kernel()
gccsd = cc.GCCSD(cell)
eccsd = gccsd.kernel()
print('Total energy per unit cell (GHF):', ehf)
print('Total energy per unit cell (GCCSD):', eccsd)

# Calculate and print the GCCSD energy based on CCSD density matrices
kpts = cell.make_kpts([1, 1, 1])
rhf = scf.RHF(cell)
uhf = scf.UHF(cell)
ghf = scf.GHF(cell)
ehf = rhf.kernel()
gccsd = cc.GCCSD(cell)
eccsd = gccsd.kernel()
print('GCCSD energy:', eccsd)