Qibochem provides the Molecule class to store the data structure of a molecule object, and to drive the classical quantum chemistry calculation to obtain necessary quantities for subsequent quantum compute calculations.

Molecule class#

class qibochem.driver.molecule.Molecule(geometry=None, charge=0, multiplicity=1, basis=None, xyz_file=None, active=None)#

Class representing a single molecule

  • geometry (list) – Molecular coordinates in OpenFermion format, e.g. [('H', (0.0, 0.0, 0.0)), ('H', (0.0, 0.0, 0.7))]

  • charge (int) – Net charge of molecule

  • multiplicity (int) – Spin multiplicity of molecule

  • basis (str) – Atomic orbital basis set, used for the PySCF/PSI4 calculations. Default: “STO-3G” (minimal basis)

  • xyz_file (str) – .xyz file containing the molecular coordinates. The comment line should follow “{charge} {multiplicity}”

  • active – Iterable representing the set of MOs to be included in the quantum simulation e.g. list(range(3,6)) for an active space with orbitals 3, 4 and 5.

Run a Hartree-Fock calculation with PySCF to obtain molecule quantities and

molecular integrals


max_scf_cycles – Maximum number of SCF cycles in PySCF

Run a Hartree-Fock calculation with PSI4 to obtain the molecular quantities and

molecular integrals


output – Name of PSI4 output file. None suppresses the output on non-Windows systems, and uses psi4_output.dat otherwise

hf_embedding(active=None, frozen=None)#
Turns on HF embedding for a given active/frozen space, and fills in the class attributes:

inactive_energy, embed_oei, and embed_tei.

  • active – Iterable representing the active-space for quantum simulation

  • frozen – Iterable representing the occupied orbitals to be removed from the simulation

hamiltonian(ham_type=None, oei=None, tei=None, constant=None, ferm_qubit_map=None)#

Builds a molecular Hamiltonian using the one-/two- electron integrals

  • ham_type – Format of molecular Hamiltonian returned. The available options are: ("f", "ferm"): OpenFermion FermionOperator, ("q", "qubit"): OpenFermion QubitOperator, or ("s", "sym"): Qibo SymbolicHamiltonian (default)

  • oei – 1-electron integrals. Default: self.oei (MO basis)

  • tei – 2-electron integrals in 2ndQ notation. Default: self.tei (MO basis)

  • constant – For inactive Fock energy if embedding used. Default: 0.0

  • ferm_qubit_map – Which fermion to qubit transformation to use. Must be either jw (default) or bk


Molecular Hamiltonian in the format of choice

static eigenvalues(hamiltonian)#
Finds the lowest 6 exact eigenvalues of the molecular Hamiltonian

Note: Uses the eigenvalues() class method for a Qibo SymbolicHamiltonian object


hamiltonian – Molecular Hamiltonian, given as a FermionOperator, QubitOperator, or SymbolicHamiltonian (not recommended)