PySCFGroundStateSolver

class PySCFGroundStateSolver(solver)

Bases: GroundStateSolver

A PySCF-based GroundStateSolver for Qiskit Nature.

This class provides a GroundStateSolver for Qiskit Nature, leveraging the fci module of PySCF. This is utility does not enable any Quantum algorithms to be used (since it replaces them in the Qiskit workflow) but instead provides a useful utility for debugging classical computational workflows based on Qiskit Nature. More importantly, it provides a more efficient implementation of what Qiskit otherwise achieves using a NumPyMinimumEigensolver in combination with a filter_criterion. For non-singlet spin ground states the setup using Qiskit components is a lot more involved, whereas this class provides an easy-to-use alternative.

Here is an example use cas:

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)

For more details please to the documentation of PySCF and Qiskit Nature.

Parameters:

solver (fci.direct_spin1.FCISolver) – a FCI solver provided by PySCF.

Attributes

qubit_mapper	Returns the qubit mapper.
solver	Returns the solver.

Methods

get_qubit_operators(problem[, aux_operators])	This solver does not deal with qubit operators and this method raises a RuntimeError.
solve(problem[, aux_operators])	Finds the ground-state of the provided problem.
supports_aux_operators()	Returns whether the eigensolver supports auxiliary operators.