4.6. Constructing a fermionic Hamiltonian with Qiskit Nature
The Qiskit Nature platform works with spin orbitals [Qiskit_Nat_1]. Each molecular orbital can have a spin-up or a spin-down electron, or spin-paired electrons. A spin orbital is either of those cases. For each molecular orbital, we have two spin orbitals. Let's now illustrate the construction of a fermionic Hamiltonian operator of the hydrogen molecule with Qiskit Nature.
4.6.1. Constructing a fermionic Hamiltonian operator of the hydrogen molecule
First, we define the molecular geometry of the hydrogen molecule with the Qiskit Molecule class, which has the following input parameters:
geometry, a list of atom names, such asHfor hydrogen, followed by Cartesian coordinates
of the atom's position in units of angstromscharge, an integer, the electric charge of the moleculemultiplicity, an integer, the multiplicity
of the molecule, where 
is the total spin angular momentum, which is determined...
