  from pyscf import gto, scf
from pyscf.pbc import gto as pbcgto
from pyscf.pbc import scf as pbcscf
from pyscf.pbc.tools import pbc

# Create cell
cell = pbcgto.Cell()
cell.atom = 'C 0.0 0.0 0.0; C 0.0 0.0 1.0'
cell.basis = 'gth-szv'
cell.pseudo = 'gth-pade'
cell.a = '4.0 4.0 4.0'
cell.unit = 'B'
cell.verbosity = 0

# Perform KHF and KMP2 calculations with 2x2x2 k-points
kpts = cell.make_kpts([2, 2, 2])
khf = pbcscf.KRHF(cell, kpts)
khf.kernel()
kmp2 = pbcscf.KMP2(khf)
kmp2.kernel()
print('KMP2 energy per unit cell:', kmp2.e_tot)

# Perform single k-point calculation using the RHF method
rhf = scf.RHF(cell)
rhf.kernel()
print('RHF energy per unit cell:', rhf.e_tot)

# Generate first and second order reduced density matrices
rdm1 = rhf.make_rdm1()
rdm2 = rhf.make_rdm2()

# Calculate total energy based on reduced density matrices
total_energy = rhf.energy_elec(rdm1, rdm2)
print('Total energy per unit cell:', total_energy)

# Convert RHF object to UHF and GHF objects
uhf = scf.UHF(cell)
uhf.kernel()
ghf = scf.GHF(cell)
ghf.kernel()

# Perform UMP2 and GMP2 calculations with 2x2x2 k-points
kpts = cell.make_kpts([2, 2, 2])
umf = pbcscf.KUMP2(uhf, kpts)
umf.kernel()
gmf = pbcscf.KGMP2(ghf, kpts)
gmf.kernel()
print('UMP2 energy per unit cell:', umf.e_tot)
print('GMP2 energy per unit cell:', gmf.e_tot)

# Generate first and second order reduced density matrices
rdm1 = umf.make_rdm1()
rdm2 = umf.make_rdm2()

# Calculate total energy based on reduced density matrices
total_energy = umf.energy_elec(rdm1, rdm2)
print('Total energy per unit cell:', total_energy)