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Update forging how-to to Qiskit Nature 0.5 #449

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Update forging how-to to Qiskit Nature 0.5 #449

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25 changes: 14 additions & 11 deletions docs/entanglement_forging/how-tos/specify-problem.rst
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Expand Up @@ -2,39 +2,42 @@
How to specify the problem
##########################

To specify the problem, we follow the Qiskit Nature workflow. We set up the ``molecule`` object, specify the driver, and instantiate the ``ElectronicStructureProblem``.
To specify the problem, we follow the Qiskit Nature workflow. We set up the ``molecule`` object, specify the driver, and instantiate the :class:`.ElectronicStructureProblem`.

We first require the following modules:

.. jupyter-execute::

from qiskit_nature.drivers import Molecule
from qiskit_nature.drivers.second_quantization import PySCFDriver
from qiskit_nature.problems.second_quantization import ElectronicStructureProblem
from qiskit_nature.second_q.formats import MoleculeInfo
from qiskit_nature.second_q.drivers import PySCFDriver
from qiskit_nature.second_q.problems import ElectronicBasis

To set up the ``molecule`` object, we specify the individual atoms and their positions:

.. jupyter-execute::

molecule = Molecule(
geometry=[
("H", [0.0, 0.0, 0.0]),
("H", [0.0, 0.0, 0.735]),
molecule = MoleculeInfo(
["H", "H"],
[
(0.0, 0.0, 0.0),
(0.0, 0.0, 0.735),
],
charge=0,
multiplicity=1, # Multiplicity (2S+1) of the molecule, where S is the total spin angular momentum
)

We then specify the driver (see ``PySCFDriver``) and load the molecule into the driver:
We then specify the driver (see :class:`.PySCFDriver`) and load the molecule into the driver:

.. jupyter-execute::

driver = PySCFDriver.from_molecule(molecule=molecule, basis="sto6g")

Here, the driver is an algorithm class that knows how to calculate the second quantized operators.

Finally, we instantiate the ``ElectronicStructureProblem``, a class which wraps a number of different types of drivers:
Finally, we instantiate the :class:`.ElectronicStructureProblem`, a class which wraps a number of different types of drivers:

.. jupyter-execute::
:stderr:
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This cell really, really wants to spit something to stderr, and the only way I could figure out not to have it cause the sphinx build to fail was to put this line here.

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Interesting, what is it printing out?

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Here's the warning:

UserWarning: Since PySCF-2.3, B3LYP (and B3P86) are changed to the VWN-RPA variant, corresponding to the original definition by Stephens et al. (issue 1480) and the same as the B3LYP functional in Gaussian. To restore the VWN5 definition, you can put the setting "B3LYP_WITH_VWN5 = True" in pyscf_conf.py

This is also showing up in some Qiskit Nature notebooks, such as at https://qiskit.org/ecosystem/nature/migration/0.5_c_electronic_structure.html.


problem = ElectronicStructureProblem(driver)
driver.run()
problem = driver.to_problem(basis=ElectronicBasis.AO)