def _compute_mp2(qmolecule, threshold):
terms = {}
mp2_delta = 0
num_particles = qmolecule.num_alpha + qmolecule.num_beta
num_orbitals = qmolecule.num_orbitals
ints = qmolecule.mo_eri_ints
oe = qmolecule.orbital_energies
# Orbital indexes given by this method are numbered according to the blocked spin ordering
singles, doubles = UCCSD.compute_excitation_lists(num_particles, num_orbitals * 2, same_spin_doubles=True)
# doubles is list of [from, to, from, to] in spin orbital indexing where alpha runs
# from 0 to num_orbitals-1, and beta from num_orbitals to num_orbitals*2-1
for n in range(len(doubles)):
idxs = doubles[n]
i = idxs[0] % num_orbitals # Since spins are same drop to MO indexing
j = idxs[2] % num_orbitals
a = idxs[1] % num_orbitals
b = idxs[3] % num_orbitals
tiajb = ints[i, a, j, b]
tibja = ints[i, b, j, a]
num = (2 * tiajb - tibja)
denom = oe[b] + oe[a] - oe[i] - oe[j]
coeff = -num / denom
coeff = coeff if abs(coeff) > threshold else 0
e_delta = coeff * tiajb
e_delta = e_delta if abs(e_delta) > threshold else 0
terms[_list_to_str(idxs)] = (coeff, e_delta)
mp2_delta += e_delta
return terms, mp2_delta
def __init__(self, operator, num_orbitals, num_particles,
qubit_mapping=None, two_qubit_reduction=False,
active_occupied=None, active_unoccupied=None,
is_eom_matrix_symmetric=True, se_list=None, de_list=None,
z2_symmetries=None, untapered_op=None):
"""Constructor.
Args:
operator (WeightedPauliOperator): qubit operator
num_orbitals (int): total number of spin orbitals
num_particles (Union(list, int)): number of particles, if it is a list,
the first number
is alpha and the second number if beta.
qubit_mapping (str): qubit mapping type
two_qubit_reduction (bool): two qubit reduction is applied or not
active_occupied (list): list of occupied orbitals to include, indices are
0 to n where n is num particles // 2
active_unoccupied (list): list of unoccupied orbitals to include, indices are
0 to m where m is (num_orbitals - num particles) // 2
is_eom_matrix_symmetric (bool): is EoM matrix symmetric
se_list (list[list]): single excitation list, overwrite the setting in active space
de_list (list[list]): double excitation list, overwrite the setting in active space
z2_symmetries (Z2Symmetries): represent the Z2 symmetries
untapered_op (WeightedPauliOperator): if the operator is tapered, we need
untapered operator
to build element of EoM matrix
"""
self._operator = operator
self._num_orbitals = num_orbitals
self._num_particles = num_particles
self._qubit_mapping = qubit_mapping
self._two_qubit_reduction = two_qubit_reduction
self._active_occupied = active_occupied
self._active_unoccupied = active_unoccupied
se_list_default, de_list_default = UCCSD.compute_excitation_lists(
self._num_particles, self._num_orbitals, self._active_occupied, self._active_unoccupied)
if se_list is None:
self._se_list = se_list_default
else:
self._se_list = se_list
logger.info("Use user-specified single excitation list: %s", self._se_list)
if de_list is None:
self._de_list = de_list_default
else:
self._de_list = de_list
logger.info("Use user-specified double excitation list: %s", self._de_list)
self._z2_symmetries = z2_symmetries if z2_symmetries is not None \
else Z2Symmetries([], [], [])
self._untapered_op = untapered_op if untapered_op is not None else operator
self._is_eom_matrix_symmetric = is_eom_matrix_symmetric
