Qiskit-nature-pyscf

New Features

- The [PySCFGroundStateSolver](https://qiskit-community.github.io/qiskit-nature-pyscf/stubs/qiskit_nature_pyscf.PySCFGroundStateSolver.html#qiskit_nature_pyscf.PySCFGroundStateSolver) now also computes the magnetization ($S^z$) and total angular momentum ($S^2$) values for all computes roots. In doing so, it properly takes the alpha-beta overlap matrix from the qiskit_nature.second_q.properties.AngularMomentum.overlap property into account. When this overlap is non-unitary, the spin-contamination within the active subspace is computed correctly. For more details, see also:
- https://github.com/qiskit-community/qiskit-nature/issues/1273
- https://github.com/qiskit-community/qiskit-nature/pull/1275
- https://github.com/qiskit-community/qiskit-nature/issues/1291
- https://github.com/qiskit-community/qiskit-nature/pull/1292

- Added support for Python 3.12.

Prelude
The use of the deprecated `qiskit.algorithms` module has been replaced by the new [qiskit-algorithms](https://github.com/qiskit community/qiskit-algorithms/) package which provide a drop-in replacement in the form of the `qiskit_algorithms` module.

New Features
- Support was added for `FCISolver` instances which have their `nroots` attribute set to a value higher than 1, indicating that they also compute excited states.

Upgrade Notes
- Support for running with Python 3.7 has been removed. You now need to use Python 3.8 as the minimum version.

Bug Fixes
- The [ElectronicDensity](https://qiskit.org/ecosystem/nature/stubs/qiskit_nature.second_q.properties.ElectronicDensity.html#qiskit_nature.second_q.properties.ElectronicDensity) object that was returned as part of the [ElectronicStructureResult](https://qiskit.org/ecosystem/nature/stubs/qiskit_nature.second_q.problems.ElectronicStructureResult.html#qiskit_nature.second_q.problems.ElectronicStructureResult) from the [PySCFGroundStateSolver](https://qiskit-community.github.io/qiskit-nature-pyscf/stubs/qiskit_nature_pyscf.PySCFGroundStateSolver.html#qiskit_nature_pyscf.PySCFGroundStateSolver) was faultily storing restricted-spin information within the alpha-spin register even though the object is documented as storing unrestricted spin-data. This has been fixed and the [ElectronicDensity](https://qiskit.org/ecosystem/nature/stubs/qiskit_nature.second_q.properties.ElectronicDensity.html#qiskit_nature.second_q.properties.ElectronicDensity) object is now guaranteed to store unrestricted-spin information. If a restricted-spin density is required it may be obtained from the [trace_spin()](https://qiskit.org/ecosystem/nature/stubs/qiskit_nature.second_q.properties.ElectronicDensity.html#qiskit_nature.second_q.properties.ElectronicDensity.trace_spin) method.

New Features

- Adds the [PySCFGroundStateSolver](https://qiskit-community.github.io/qiskit-nature-pyscf/stubs/qiskit_nature_pyscf.PySCFGroundStateSolver.html#qiskit_nature_pyscf.PySCFGroundStateSolver) to provide simpler means for testing and debugging classical computational workflows in Qiskit Nature. Below is an example of how to use it:

python
from pyscf import fci

from qiskit_nature.second_q.drivers import MethodType, PySCFDriver
from qiskit_nature.second_q.transformers import ActiveSpaceTransformer

from qiskit_nature_pyscf import PySCFGroundStateSolver

driver = PySCFDriver(
atom="O 0.0 0.0 0.0; O 0.0 0.0 1.5",
basis="sto3g",
spin=2,
method=MethodType.UHF,
)
problem = driver.run()

transformer = ActiveSpaceTransformer(4, 4)

problem = transformer.transform(problem)

solver = PySCFGroundStateSolver(fci.direct_uhf.FCI())

result = solver.solve(problem)
print(result)


- Added support for running with Python 3.11.

Bug Fixes
- Ensures compatibility of this plugin with Qiskit Nature 0.6. The examples are updated in order to avoid triggering deprecation warnings. Using Qiskit Nature 0.5 is still supported.

Bug Fixes

- Ensures compatibility of this plugin with Qiskit Nature 0.6. The examples are updated in order to avoid triggering deprecation warnings. Using Qiskit Nature 0.5 is still supported.