refactor: Towards a non-driver future

As outlined in qiskit-community#701, Qiskit Nature is working towards a non-driver focused future. This means, rather than the `BaseProblem` interface taking in a `BaseDriver` and an optional list of `BaseTransformer` instances, the problem itself should be a fully standalone description of the user's problem of interest. In other words, `BaseProblem` should be the produced result of a `BaseDriver` and, by extension, `BaseTransformer` instances should transform problem instances. This commit works towards such a future by refactoring the code: - `BaseProblem` is the returned object of `BaseDriver.run` - `BaseTransformer.transform` has `BaseProblem` as in- and output - `BaseProblem` takes over the role of `GroupedProperty` - in doing so, `Hamiltonian` objects are more clearly separated from `Property` objects (further refactoring to come)
mrossinek · Jul 21, 2022 · 271305e · 271305e
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diff --git a/README.md b/README.md
@@ -68,7 +68,6 @@ the ground-state (minimum) energy of a molecule.
 from qiskit_nature.settings import settings
 from qiskit_nature.second_q.drivers import UnitsType
 from qiskit_nature.second_q.drivers import PySCFDriver
-from qiskit_nature.second_q.problems import ElectronicStructureProblem
 
 settings.dict_aux_operators = True
 
@@ -78,13 +77,12 @@ settings.dict_aux_operators = True
 driver = PySCFDriver(atom='H .0 .0 .0; H .0 .0 0.735',
                      unit=UnitsType.ANGSTROM,
                      basis='sto3g')
-problem = ElectronicStructureProblem(driver)
+problem = driver.run()
 
 # generate the second-quantized operators
-second_q_ops = problem.second_q_ops()
-main_op = second_q_ops['ElectronicEnergy']
+main_op, aux_ops = problem.second_q_ops()
 
-particle_number = problem.grouped_property_transformed.get_property("ParticleNumber")
+particle_number = problem.properties["ParticleNumber"]
 
 num_particles = (particle_number.num_alpha, particle_number.num_beta)
 num_spin_orbitals = particle_number.num_spin_orbitals

diff --git a/docs/tutorials/01_electronic_structure.ipynb b/docs/tutorials/01_electronic_structure.ipynb
@@ -156,7 +156,6 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "from qiskit_nature.second_q.problems import ElectronicStructureProblem\n",
     "from qiskit_nature.second_q.mappers import QubitConverter\n",
     "from qiskit_nature.second_q.mappers import JordanWignerMapper, ParityMapper"
    ]
@@ -188,9 +187,9 @@
     }
    ],
    "source": [
-    "es_problem = ElectronicStructureProblem(driver)\n",
-    "second_q_op = es_problem.second_q_ops()\n",
-    "print(second_q_op[0])"
+    "es_problem = driver.run()\n",
+    "main_op, second_q_ops = es_problem.second_q_ops()\n",
+    "print(main_op)"
    ]
   },
   {

diff --git a/docs/tutorials/02_vibrational_structure.ipynb b/docs/tutorials/02_vibrational_structure.ipynb
@@ -196,12 +196,13 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "from qiskit_nature.second_q.problems import VibrationalStructureProblem\n",
     "from qiskit_nature.second_q.mappers import QubitConverter\n",
     "from qiskit_nature.second_q.mappers import DirectMapper\n",
     "\n",
-    "vibrational_problem = VibrationalStructureProblem(driver, num_modals=2, truncation_order=2)\n",
-    "second_q_ops = vibrational_problem.second_q_ops()"
+    "vibrational_problem = driver.run()\n",
+    "vibrational_problem.num_modals = 2\n",
+    "vibrational_problem.truncation_order = 2\n",
+    "main_op, second_q_ops = vibrational_problem.second_q_ops()"
    ]
   },
   {
@@ -270,7 +271,7 @@
     }
    ],
    "source": [
-    "print(second_q_ops[0])"
+    "print(main_op)"
    ]
   },
   {
@@ -342,7 +343,7 @@
    ],
    "source": [
     "qubit_converter = QubitConverter(mapper=DirectMapper())\n",
-    "qubit_op = qubit_converter.convert(second_q_ops[0])\n",
+    "qubit_op = qubit_converter.convert(main_op)\n",
     "\n",
     "print(qubit_op)"
    ]
@@ -610,12 +611,14 @@
     }
    ],
    "source": [
-    "vibrational_problem = VibrationalStructureProblem(driver, num_modals=3, truncation_order=2)\n",
-    "second_q_ops = vibrational_problem.second_q_ops()\n",
+    "vibrational_problem = driver.run()\n",
+    "vibrational_problem.num_modals = 3\n",
+    "vibrational_problem.truncation_order = 2\n",
+    "main_op, second_q_ops = vibrational_problem.second_q_ops()\n",
     "\n",
     "qubit_converter = QubitConverter(mapper=DirectMapper())\n",
     "\n",
-    "qubit_op = qubit_converter.convert(second_q_ops[0])\n",
+    "qubit_op = qubit_converter.convert(main_op)\n",
     "\n",
     "print(qubit_op)"
    ]

diff --git a/docs/tutorials/03_ground_state_solvers.ipynb b/docs/tutorials/03_ground_state_solvers.ipynb
@@ -32,7 +32,6 @@
     "    ElectronicStructureDriverType,\n",
     "    ElectronicStructureMoleculeDriver,\n",
     ")\n",
-    "from qiskit_nature.second_q.problems import ElectronicStructureProblem\n",
     "from qiskit_nature.second_q.mappers import QubitConverter\n",
     "from qiskit_nature.second_q.mappers import JordanWignerMapper\n",
     "\n",
@@ -43,7 +42,7 @@
     "    molecule, basis=\"sto3g\", driver_type=ElectronicStructureDriverType.PYSCF\n",
     ")\n",
     "\n",
-    "es_problem = ElectronicStructureProblem(driver)\n",
+    "es_problem = driver.run()\n",
     "qubit_converter = QubitConverter(JordanWignerMapper())"
    ]
   },
@@ -276,12 +275,13 @@
    "source": [
     "from qiskit_nature.second_q.drivers import GaussianForcesDriver\n",
     "from qiskit_nature.second_q.algorithms import NumPyMinimumEigensolverFactory\n",
-    "from qiskit_nature.second_q.problems import VibrationalStructureProblem\n",
     "from qiskit_nature.second_q.mappers import DirectMapper\n",
     "\n",
     "driver = GaussianForcesDriver(logfile=\"aux_files/CO2_freq_B3LYP_631g.log\")\n",
     "\n",
-    "vib_problem = VibrationalStructureProblem(driver, num_modals=2, truncation_order=2)\n",
+    "vib_problem = driver.run()\n",
+    "vib_problem.num_modals = 2\n",
+    "vib_problem.truncation_order = 2\n",
     "\n",
     "qubit_covnerter = QubitConverter(DirectMapper())\n",
     "\n",

diff --git a/docs/tutorials/04_excited_states_solvers.ipynb b/docs/tutorials/04_excited_states_solvers.ipynb
@@ -47,7 +47,6 @@
     "    ElectronicStructureDriverType,\n",
     "    ElectronicStructureMoleculeDriver,\n",
     ")\n",
-    "from qiskit_nature.second_q.problems import ElectronicStructureProblem\n",
     "from qiskit_nature.second_q.mappers import QubitConverter\n",
     "from qiskit_nature.second_q.mappers import JordanWignerMapper\n",
     "\n",
@@ -58,7 +57,7 @@
     "    molecule, basis=\"sto3g\", driver_type=ElectronicStructureDriverType.PYSCF\n",
     ")\n",
     "\n",
-    "es_problem = ElectronicStructureProblem(driver)\n",
+    "es_problem = driver.run()\n",
     "qubit_converter = QubitConverter(JordanWignerMapper())"
    ]
   },

diff --git a/docs/tutorials/07_leveraging_qiskit_runtime.ipynb b/docs/tutorials/07_leveraging_qiskit_runtime.ipynb
@@ -53,7 +53,6 @@
     "    ElectronicStructureDriverType,\n",
     "    ElectronicStructureMoleculeDriver,\n",
     ")\n",
-    "from qiskit_nature.second_q.problems import ElectronicStructureProblem\n",
     "from qiskit_nature.second_q.mappers import QubitConverter\n",
     "from qiskit_nature.second_q.mappers import ParityMapper\n",
     "from qiskit_nature.second_q.properties import ParticleNumber\n",
@@ -88,7 +87,8 @@
     ")\n",
     "\n",
     "# define electronic structure problem\n",
-    "problem = ElectronicStructureProblem(driver, transformers=[active_space_trafo])\n",
+    "problem = driver.run()\n",
+    "problem = active_space_trafo.transform(problem)",
     "\n",
     "# construct qubit converter (parity mapping + 2-qubit reduction)\n",
     "qubit_converter = QubitConverter(ParityMapper(), two_qubit_reduction=True)"

diff --git a/docs/tutorials/10_lattice_models.ipynb b/docs/tutorials/10_lattice_models.ipynb
@@ -921,7 +921,7 @@
     "    onsite_interaction=u,\n",
     ")\n",
     "\n",
-    "lmp = LatticeModelProblem(lattice_model=fhm)"
+    "lmp = LatticeModelProblem(fhm)"
    ]
   },
   {
@@ -1021,4 +1021,4 @@
  },
  "nbformat": 4,
  "nbformat_minor": 4
-}
+}
diff --git a/qiskit_nature/second_q/algorithms/excited_states_solvers/excited_states_eigensolver.py b/qiskit_nature/second_q/algorithms/excited_states_solvers/excited_states_eigensolver.py
@@ -65,20 +65,7 @@ def get_qubit_operators(
         """Gets the operator and auxiliary operators, and transforms the provided auxiliary operators"""
         # Note that ``aux_ops`` contains not only the transformed ``aux_operators`` passed by the
         # user but also additional ones from the transformation
-        second_q_ops = problem.second_q_ops()
-        aux_second_q_ops: ListOrDictType[SecondQuantizedOp]
-        if isinstance(second_q_ops, list):
-            main_second_q_op = second_q_ops[0]
-            aux_second_q_ops = second_q_ops[1:]
-        elif isinstance(second_q_ops, dict):
-            name = problem.main_property_name
-            main_second_q_op = second_q_ops.pop(name, None)
-            if main_second_q_op is None:
-                raise ValueError(
-                    f"The main `SecondQuantizedOp` associated with the {name} property cannot be "
-                    "`None`."
-                )
-            aux_second_q_ops = second_q_ops
+        main_second_q_op, aux_second_q_ops = problem.second_q_ops()
 
         main_operator = self._qubit_converter.convert(
             main_second_q_op,

diff --git a/qiskit_nature/second_q/algorithms/excited_states_solvers/qeom.py b/qiskit_nature/second_q/algorithms/excited_states_solvers/qeom.py
@@ -117,11 +117,7 @@ def solve(
         groundstate_result = self._gsc.solve(problem, aux_operators)
 
         # 2. Prepare the excitation operators
-        second_q_ops = problem.second_q_ops()
-        if isinstance(second_q_ops, list):
-            main_second_q_op = second_q_ops[0]
-        elif isinstance(second_q_ops, dict):
-            main_second_q_op = second_q_ops.pop(problem.main_property_name)
+        main_second_q_op, _ = problem.second_q_ops()
 
         self._untapered_qubit_op_main = self._gsc.qubit_converter.convert_only(
             main_second_q_op, problem.num_particles

diff --git a/qiskit_nature/second_q/algorithms/ground_state_solvers/adapt_vqe.py b/qiskit_nature/second_q/algorithms/ground_state_solvers/adapt_vqe.py
@@ -211,21 +211,7 @@ def solve(
             information about the AdaptVQE algorithm like the number of iterations, finishing
             criterion, and the final maximum gradient.
         """
-        second_q_ops = problem.second_q_ops()
-
-        aux_second_q_ops: ListOrDictType[SecondQuantizedOp]
-        if isinstance(second_q_ops, list):
-            main_second_q_op = second_q_ops[0]
-            aux_second_q_ops = second_q_ops[1:]
-        elif isinstance(second_q_ops, dict):
-            name = problem.main_property_name
-            main_second_q_op = second_q_ops.pop(name, None)
-            if main_second_q_op is None:
-                raise ValueError(
-                    f"The main `SecondQuantizedOp` associated with the {name} property cannot be "
-                    "`None`."
-                )
-            aux_second_q_ops = second_q_ops
+        main_second_q_op, aux_second_q_ops = problem.second_q_ops()
 
         self._main_operator = self._qubit_converter.convert(
             main_second_q_op,

diff --git a/qiskit_nature/second_q/algorithms/ground_state_solvers/ground_state_eigensolver.py b/qiskit_nature/second_q/algorithms/ground_state_solvers/ground_state_eigensolver.py
@@ -101,20 +101,8 @@ def get_qubit_operators(
         """Gets the operator and auxiliary operators, and transforms the provided auxiliary operators"""
         # Note that ``aux_ops`` contains not only the transformed ``aux_operators`` passed by the
         # user but also additional ones from the transformation
-        second_q_ops = problem.second_q_ops()
-        aux_second_q_ops: ListOrDictType[SecondQuantizedOp]
-        if isinstance(second_q_ops, list):
-            main_second_q_op = second_q_ops[0]
-            aux_second_q_ops = second_q_ops[1:]
-        elif isinstance(second_q_ops, dict):
-            name = problem.main_property_name
-            main_second_q_op = second_q_ops.pop(name, None)
-            if main_second_q_op is None:
-                raise ValueError(
-                    f"The main `SecondQuantizedOp` associated with the {name} property cannot be "
-                    "`None`."
-                )
-            aux_second_q_ops = second_q_ops
+        main_second_q_op, aux_second_q_ops = problem.second_q_ops()
+
         main_operator = self._qubit_converter.convert(
             main_second_q_op,
             num_particles=problem.num_particles,

diff --git a/...second_q/algorithms/ground_state_solvers/minimum_eigensolver_factories/vqe_ucc_factory.py b/...second_q/algorithms/ground_state_solvers/minimum_eigensolver_factories/vqe_ucc_factory.py
@@ -276,8 +276,7 @@ def get_solver(  # type: ignore[override]
         Returns:
             A VQE suitable to compute the ground state of the molecule.
         """
-        driver_result = problem.grouped_property_transformed
-        particle_number = cast(ParticleNumber, driver_result.get_property(ParticleNumber))
+        particle_number = cast(ParticleNumber, problem.properties["ParticleNumber"])
         num_spin_orbitals = particle_number.num_spin_orbitals
         num_particles = particle_number.num_alpha, particle_number.num_beta
 
@@ -296,7 +295,7 @@ def get_solver(  # type: ignore[override]
 
         if isinstance(self.initial_point, InitialPoint):
             self.initial_point.ansatz = ansatz
-            self.initial_point.grouped_property = driver_result
+            self.initial_point.grouped_property = problem
             initial_point = self.initial_point.to_numpy_array()
         else:
             initial_point = self.initial_point

diff --git a/...econd_q/algorithms/ground_state_solvers/minimum_eigensolver_factories/vqe_uvcc_factory.py b/...econd_q/algorithms/ground_state_solvers/minimum_eigensolver_factories/vqe_uvcc_factory.py
@@ -13,7 +13,7 @@
 """The minimum eigensolver factory for ground state calculation algorithms."""
 
 import logging
-from typing import Optional, Union, Callable, cast
+from typing import Optional, Union, Callable
 import numpy as np
 
 from qiskit.algorithms import MinimumEigensolver, VQE
@@ -27,9 +27,6 @@
 from qiskit_nature.second_q.problems import (
     VibrationalStructureProblem,
 )
-from qiskit_nature.second_q.properties import (
-    VibrationalStructureDriverResult,
-)
 from qiskit_nature.deprecation import deprecate_property, deprecate_positional_arguments
 
 from .minimum_eigensolver_factory import MinimumEigensolverFactory
@@ -265,7 +262,7 @@ def get_solver(  # type: ignore[override]
             A VQE suitable to compute the ground state of the molecule.
         """
 
-        basis = cast(VibrationalStructureDriverResult, problem.grouped_property_transformed).basis
+        basis = problem.basis
         num_modals = basis.num_modals_per_mode
         num_modes = len(num_modals)
 

diff --git a/qiskit_nature/second_q/algorithms/initial_points/hf_initial_point.py b/qiskit_nature/second_q/algorithms/initial_points/hf_initial_point.py
@@ -20,9 +20,7 @@
 
 from qiskit_nature.second_q.circuit.library import UCC
 from qiskit_nature.second_q.properties import ElectronicEnergy
-from qiskit_nature.second_q.properties.second_quantized_property import (
-    GroupedSecondQuantizedProperty,
-)
+from qiskit_nature.second_q.problems import BaseProblem
 from qiskit_nature.exceptions import QiskitNatureError
 
 from .initial_point import InitialPoint
@@ -50,7 +48,7 @@ def __init__(self) -> None:
         self._parameters: np.ndarray | None = None
 
     @property
-    def grouped_property(self) -> GroupedSecondQuantizedProperty | None:
+    def grouped_property(self) -> BaseProblem | None:
         """The grouped property.
 
         The grouped property is not required to compute the HF initial point. If it is provided we
@@ -59,9 +57,9 @@ def grouped_property(self) -> GroupedSecondQuantizedProperty | None:
         return self._grouped_property
 
     @grouped_property.setter
-    def grouped_property(self, grouped_property: GroupedSecondQuantizedProperty) -> None:
-        electronic_energy: ElectronicEnergy | None = grouped_property.get_property(ElectronicEnergy)
-        if electronic_energy is None:
+    def grouped_property(self, grouped_property: BaseProblem) -> None:
+        electronic_energy = grouped_property.hamiltonian
+        if electronic_energy is None or not isinstance(electronic_energy, ElectronicEnergy):
             warnings.warn(
                 "The ElectronicEnergy was not obtained from the grouped_property. "
                 "The grouped_property and reference_energy will not be set."
@@ -115,7 +113,7 @@ def to_numpy_array(self) -> np.ndarray:
     def compute(
         self,
         ansatz: UCC | None = None,
-        grouped_property: GroupedSecondQuantizedProperty | None = None,
+        grouped_property: BaseProblem | None = None,
     ) -> None:
         """Compute the coefficients and energy corrections.
 

diff --git a/qiskit_nature/second_q/algorithms/initial_points/initial_point.py b/qiskit_nature/second_q/algorithms/initial_points/initial_point.py
@@ -19,9 +19,7 @@
 import numpy as np
 
 from qiskit.circuit.library import EvolvedOperatorAnsatz
-from qiskit_nature.second_q.properties.second_quantized_property import (
-    GroupedSecondQuantizedProperty,
-)
+from qiskit_nature.second_q.problems import BaseProblem
 
 
 class InitialPoint(ABC):
@@ -34,7 +32,7 @@ class InitialPoint(ABC):
     @abstractmethod
     def __init__(self):
         self._ansatz: EvolvedOperatorAnsatz | None = None
-        self._grouped_property: GroupedSecondQuantizedProperty | None = None
+        self._grouped_property: BaseProblem | None = None
 
     @property
     @abstractmethod
@@ -51,7 +49,7 @@ def ansatz(self, ansatz: EvolvedOperatorAnsatz) -> None:
         raise NotImplementedError
 
     @property
-    def grouped_property(self) -> GroupedSecondQuantizedProperty | None:
+    def grouped_property(self) -> BaseProblem | None:
         """The grouped property.
 
         Raises:
@@ -60,7 +58,7 @@ def grouped_property(self) -> GroupedSecondQuantizedProperty | None:
         raise NotImplementedError
 
     @grouped_property.setter
-    def grouped_property(self, grouped_property: GroupedSecondQuantizedProperty) -> None:
+    def grouped_property(self, grouped_property: BaseProblem) -> None:
         raise NotImplementedError
 
     @abstractmethod
@@ -75,7 +73,7 @@ def to_numpy_array(self) -> np.ndarray:
     def compute(
         self,
         ansatz: EvolvedOperatorAnsatz | None = None,
-        grouped_property: GroupedSecondQuantizedProperty | None = None,
+        grouped_property: BaseProblem | None = None,
     ) -> None:
         """Compute the initial point array"""
         raise NotImplementedError