4.8. Constructing a qubit Hamiltonian operator with Qiskit Nature

This section shows how to construct a qubit Hamiltonian operator with Qiskit Nature for the hydrogen molecule and the lithium hydride molecule.

We define the fermion_to_qubit() function to convert a fermionic operator to a qubit operator, which has the following input parameters:

• f_op, a fermionic operator obtained as explained in Section 4.6, Constructing a fermionic Hamiltonian with Qiskit Nature
• mapper, either "Jordan-Wigner" or "Parity" or "Bravyi-Kitaev"
• truncate, an integer to truncate the display of the Pauli list, which can be very large; set to 20 items by default
• two_qubit_reduction, Boolean, by default False, that determines whether to carry out two-qubit reduction when possible
• z2symmetry_reduction, by default None, that indicates whether a Z2 symmetry reduction should be applied to resulting qubit operators that are computed based on mathematical symmetries...