import os
from pyscf import gto, scf, dmrgscf, mrpt
from pyscf.mcscf import avas

# --- system ---
xyz = """
C  -1.88130994142197  -0.01841437035529  -2.22287428411536
C   1.72895548079486   0.45194023954643   1.20418711485103
H  -2.50443875532784  -0.09124514525132  -1.32927474964013
H  -1.14399357284048   0.70714156089601  -2.57231771124877
H   0.99092973158558  -0.27314004685281   1.55312184466584
H   2.35214705720987   0.52473776201696   0.31062778548742
"""

mol = gto.M(atom=xyz, unit="Angstrom", basis="sto-3g", symmetry=False, verbose=4)
mf = scf.RHF(mol).run()

# --- AVAS active space (valence) ---
ao_labels = ['C 2s', 'C 2p']
avas_obj = avas.AVAS(mf, ao_labels)
norb_cas, nelec_cas, mo_avas = avas_obj.kernel()

# --- DMRGSCF (Block2) ---
dmrgscf.settings.BLOCKEXE   = os.popen("which block2main").read().strip()
dmrgscf.settings.MPIPREFIX  = "mpirun -n 16" 

mc = dmrgscf.DMRGSCF(mf, norb_cas, nelec_cas, maxM=300, tol=1e-6)
mc.mo_coeff = mo_avas
E_cas = mc.kernel()[0]
print("E(DMRGSCF) =", E_cas)

# --- NEVPT2 ---
E_corr = mrpt.NEVPT(mc, root=0).kernel()    # may still try to use the old launcher
print("NEVPT2 correction =", E_corr)
print("E(total) =", E_cas + E_corr)

******** <class 'pyscf.mrpt.nevpt2.NEVPT'> ********
NEVPT2 (6e+6e, 8o), ncore = 2, nvir = 4
root = 0

WARN: Active orbitals [0 1] (occs = [2. 2.]) are canonicalized with core orbitals

FCI vector not available, call CASCI to update wavefunction
Natural occ [2.         2.         1.99999889 1.99999883 1.00135169 1.00015386
 0.99984666 0.99865008]
Natural orbital (expansion on meta-Lowdin AOs) in CAS space
               #1        #2        #3        #4        #5       
0 C 1s          -0.00005  -0.00001   0.00465   0.00704   0.00035
0 C 2s           0.09830  -0.00059   0.49781   0.50266  -0.19997
...
...
...
<CAS-nat-orb|mo-hf>  10     8        0.64380022
<CAS-nat-orb|mo-hf>  10     10       0.76376330
DMRG-NEVPT
......production of RDMs took       3.39 sec
......reading the RDM took          0.37 sec

# --- DMRGSCF (Block2) ---
dmrgscf.settings.BLOCKEXE   = os.popen("which block2main").read().strip()
dmrgscf.settings.BLOCKEXE_COMPRESS_NEVPT = os.popen("which block2main").read().strip()
dmrgscf.settings.MPIPREFIX  = "mpirun -n 8" 

mc = dmrgscf.DMRGSCF(mf, norb_cas, nelec_cas, maxM=200, tol=1e-6)
mc.mo_coeff = mo_avas
E_cas = mc.kernel()[0]

# --- NEVPT2 ---
E_corr = mrpt.NEVPT(mc, root=0).compress_approx(maxM=200).kernel()