qml.qchem

The PennyLane quantum chemistry library.

Note

To access the qml.qchem package, pennylane-qchem must be installed via pip:

pip install pennylane-qchem

The PennyLane quantum chemistry package. Supports OpenFermion, PySCF, and Psi4 for quantum chemistry calculations using PennyLane.

Functions

read_structure(filepath[, outpath])	Reads the structure of the polyatomic system from a file and returns a list with the symbols of the atoms in the molecule and a 1D array with their positions \([x_1, y_1, z_1, x_2, y_2, z_2, \dots]\) in atomic units (Bohr radius = 1).
meanfield(symbols, coordinates[, name, …])	Generates a file from which the mean field electronic structure of the molecule can be retrieved.
active_space(electrons, orbitals[, mult, …])	Builds the active space for a given number of active electrons and active orbitals.
decompose(hf_file[, mapping, core, active])	Decomposes the molecular Hamiltonian into a linear combination of Pauli operators using OpenFermion tools.
convert_observable(qubit_observable[, wires])	Converts an OpenFermion QubitOperator operator to a Pennylane VQE observable
molecular_hamiltonian(symbols, coordinates)	Generates the qubit Hamiltonian of a molecule.
hf_state(electrons, orbitals)	Generates the occupation-number vector representing the Hartree-Fock state.
excitations(electrons, orbitals[, delta_sz])	Generates single and double excitations from a Hartree-Fock reference state.
excitations_to_wires(singles, doubles[, wires])	Map the indices representing the single and double excitations generated with the function excitations() to the wires that the Unitary Coupled-Cluster (UCCSD) template will act on.
_qubit_operator_to_terms(qubit_operator[, wires])	Converts OpenFermion QubitOperator to a 2-tuple of coefficients and PennyLane Pauli observables.
_terms_to_qubit_operator(coeffs, ops[, wires])	Converts a 2-tuple of complex coefficients and PennyLane operations to OpenFermion QubitOperator.
_qubit_operators_equivalent(…[, wires])	Checks equivalence between OpenFermion QubitOperator and Pennylane VQE Hamiltonian (Tensor product of Pauli matrices).

qml.qchem.obs

This module contains functions to construct many-body observables whose expectation values can be used to simulate molecular properties.

observable(fermion_ops[, init_term, …])	Builds the Fermion many-body observable whose expectation value can be measured in PennyLane.
particle_number(orbitals[, mapping, wires])	Computes the particle number operator \(\hat{N}=\sum_\alpha \hat{n}_\alpha\) in the Pauli basis.
spin_z(orbitals[, mapping, wires])	Computes the total spin projection operator \(\hat{S}_z\) in the Pauli basis.
spin2(electrons, orbitals[, mapping, wires])	Computes the total spin operator \(\hat{S}^2\).
one_particle(matrix_elements[, core, …])	Generates the FermionOperator representing a given one-particle operator required to build many-body qubit observables.
two_particle(matrix_elements[, core, …])	Generates the FermionOperator representing a given two-particle operator required to build many-body qubit observables.
_spin2_matrix_elements(sz)	Builds the table of matrix elements \(\langle \bm{\alpha}, \bm{\beta} \vert \hat{s}_1 \cdot \hat{s}_2 \vert \bm{\gamma}, \bm{\delta} \rangle\) of the two-particle spin operator \(\hat{s}_1 \cdot \hat{s}_2\).