Merge pull request #86 from qiboteam/refactor-ansatzes

Refactor code for some ansatzes

doc/source/api-reference/ansatz.rst

@@ -2,12 +2,12 @@
 Ansatz
 ======
 
-This section covers the API reference for various chemistry ansatzes.
+This section covers the API reference for various chemistry circuit ansatzes.
 
 Hardware-efficient
 ------------------
 
-.. autofunction:: qibochem.ansatz.hardware_efficient.hea
+.. autofunction:: qibochem.ansatz.hardware_efficient.he_circuit
 
 
 Hartree-Fock

doc/source/getting-started/quickstart.rst

@@ -15,8 +15,7 @@ Here is an example of building the UCCD ansatz with the H2 molecule to test your
     from qibo.models import VQE
 
     from qibochem.driver.molecule import Molecule
-    from qibochem.ansatz.hf_reference import hf_circuit
-    from qibochem.ansatz.ucc import ucc_circuit
+    from qibochem.ansatz import hf_circuit, ucc_circuit
 
     # Define the H2 molecule and obtain its 1-/2- electron integrals with PySCF
     h2 = Molecule([('H', (0.0, 0.0, 0.0)), ('H', (0.0, 0.0, 0.7))])

doc/source/tutorials/ansatz.rst

@@ -16,17 +16,12 @@ For the H\ :sub:`2` case discussed in previous sections, a possible hardware eff
 
 .. code-block:: python
 
-    from qibo import Circuit
+    from qibochem.ansatz import he_circuit
 
-    from qibochem.ansatz import hardware_efficient
-
-    nlayers = 1
     nqubits = 4
-    nfermions = 2
+    nlayers = 1
 
-    circuit = Circuit(4)
-    hardware_efficient_ansatz = hardware_efficient.hea(nlayers, nqubits)
-    circuit.add(hardware_efficient_ansatz)
+    circuit = he_circuit(nqubits, nlayers)
     print(circuit.draw())
 
 .. code-block:: output
@@ -43,11 +38,10 @@ The following example demonstrates how the energy of the H2 molecule is affected
 .. code-block:: python
 
     import numpy as np
-    from qibo import Circuit
 
-    from qibochem.driver.molecule import Molecule
+    from qibochem.driver import Molecule
     from qibochem.measurement.expectation import expectation
-    from qibochem.ansatz import hardware_efficient
+    from qibochem.ansatz import he_circuit
 
     mol = Molecule([("H", (0.0, 0.0, 0.0)), ("H", (0.0, 0.0, 0.74804))])
     mol.run_pyscf()
@@ -57,10 +51,7 @@ The following example demonstrates how the energy of the H2 molecule is affected
     nlayers = 1
     nqubits = mol.nso
     ntheta = 2 * nqubits * nlayers
-    hea_ansatz = hardware_efficient.hea(nlayers, nqubits)
-
-    circuit = Circuit(nqubits)
-    circuit.add(hea_ansatz)
+    circuit = he_circuit(nqubits, nlayers)
 
     print("Energy expectation values for thetas: ")
     print("-----------------------------")
@@ -116,8 +107,7 @@ An example of how to build a UCC doubles circuit ansatz for the :math:`H_2` mole
 .. code-block:: python
 
     from qibochem.driver.molecule import Molecule
-    from qibochem.ansatz.hf_reference import hf_circuit
-    from qibochem.ansatz.ucc import ucc_circuit
+    from qibochem.ansatz import hf_circuit, ucc_circuit
 
     mol = Molecule([("H", (0.0, 0.0, 0.0)), ("H", (0.0, 0.0, 0.74804))])
     mol.run_pyscf()

examples/br_example.py

@@ -4,21 +4,15 @@
 """
 
 import numpy as np
-from qibo import Circuit, gates, models
-from qibo.optimizers import optimize
-from scipy.optimize import minimize
+from qibo.models import VQE
 
-from qibochem.ansatz import basis_rotation
-from qibochem.ansatz.hf_reference import hf_circuit
-from qibochem.driver.molecule import Molecule
+from qibochem.ansatz import basis_rotation, hf_circuit
+from qibochem.driver import Molecule
 from qibochem.measurement.expectation import expectation
 
 # Define molecule and populate
 mol = Molecule(xyz_file="h3p.xyz")
-try:
-    mol.run_pyscf()
-except ModuleNotFoundError:
-    mol.run_psi4()
+mol.run_pyscf()
 
 # Diagonalize H_core to use as the guess wave function
 
@@ -59,16 +53,14 @@ def basis_rotation_circuit(mol, parameters=0.0):
     gate_layout = basis_rotation.basis_rotation_layout(nqubits)
     gate_list, ordered_angles = basis_rotation.basis_rotation_gates(gate_layout, gate_angles, theta)
 
-    circuit = Circuit(nqubits)
-    for _i in range(mol.nelec):
-        circuit.add(gates.X(_i))
+    circuit = hf_circuit(nqubits, mol.nelec)
     circuit.add(gate_list)
 
     return circuit, gate_angles
 
 
 br_circuit, qubit_parameters = basis_rotation_circuit(mol, parameters=0.1)
-vqe = models.VQE(br_circuit, hamiltonian)
+vqe = VQE(br_circuit, hamiltonian)
 vqe_result = vqe.minimize(qubit_parameters)
 
 print(f" HF energy: {mol.e_hf:.8f}")

examples/ucc_example1.py

@@ -6,22 +6,18 @@
 from qibo.optimizers import optimize
 from scipy.optimize import minimize
 
-from qibochem.ansatz.hf_reference import hf_circuit
-from qibochem.ansatz.ucc import ucc_circuit
+from qibochem.ansatz import hf_circuit, ucc_circuit
 from qibochem.driver.molecule import Molecule
 from qibochem.measurement.expectation import expectation
 
 # Define molecule and populate
 mol = Molecule(xyz_file="lih.xyz")
-try:
-    mol.run_pyscf()
-except ModuleNotFoundError:
-    mol.run_psi4()
+mol.run_pyscf()
 
 
 # Apply embedding and boson encoding
 mol.hf_embedding(active=[1, 2, 5])
-hamiltonian = mol.hamiltonian(oei=mol.embed_oei, tei=mol.embed_tei, constant=mol.inactive_energy)
+hamiltonian = mol.hamiltonian()
 
 # Set parameters for the rest of the experiment
 n_qubits = mol.n_active_orbs
@@ -56,11 +52,8 @@
 n_unique_excitations = 5
 
 # UCCSD: Circuit
-all_coeffs = []
 for _ex in excitations:
-    coeffs = []
-    circuit += ucc_circuit(n_qubits, _ex, coeffs=coeffs)
-    all_coeffs.append(coeffs)
+    circuit += ucc_circuit(n_qubits, _ex)
 
 # Draw the circuit if interested
 print(circuit.draw())
@@ -71,19 +64,28 @@ def electronic_energy(parameters):
     r"""
     Loss function for the UCCSD ansatz
     """
-    all_parameters = []
+    coeff_dict = {1: (-1.0, 1.0), 2: (-0.25, 0.25, 0.25, 0.25, -0.25, -0.25, -0.25, 0.25)}
 
-    # UCC parameters
-    # Expand the parameters to match the total UCC ansatz manually
-    _ucc = parameters[:n_unique_excitations]
+    # Unique UCC parameters
     # Manually group the related excitations together
-    ucc_parameters = [_ucc[0], _ucc[1], _ucc[2], _ucc[2], _ucc[3], _ucc[3], _ucc[4], _ucc[4]]
-    # Need to iterate through each excitation this time
-    for _coeffs, _parameter in zip(all_coeffs, ucc_parameters):
+    ucc_parameters = [
+        parameters[0],
+        parameters[1],
+        parameters[2],
+        parameters[2],
+        parameters[3],
+        parameters[3],
+        parameters[4],
+        parameters[4],
+    ]
+    all_parameters = []
+    # Iterate through each excitation, with the list of coefficients dependent on whether S/D excitation
+    for _ex, _parameter in zip(excitations, ucc_parameters):
+        coeffs = coeff_dict[len(_ex) // 2]
         # Convert a single value to a array with dimension=n_param_gates
-        ucc_parameter = np.repeat(_parameter, len(_coeffs))
+        ucc_parameter = np.repeat(_parameter, len(coeffs))
         # Multiply by coeffs
-        ucc_parameter *= _coeffs
+        ucc_parameter *= coeffs
         all_parameters.append(ucc_parameter)
 
     # Flatten all_parameters into a single list to set the circuit parameters
@@ -101,7 +103,7 @@ def electronic_energy(parameters):
 
 best, params, extra = optimize(electronic_energy, params)
 
-print("\nResults using Qibo optimize:")
+print("\nResults using Qibo optimize: (With HF embedding)")
 print(f"FCI energy: {fci_energy:.8f}")
 print(f" HF energy: {mol.e_hf:.8f} (Classical)")
 print(f"VQE energy: {best:.8f} (UCCSD ansatz)")
@@ -115,15 +117,15 @@ def electronic_energy(parameters):
 result = minimize(electronic_energy, params)
 best, params = result.fun, result.x
 
-print("\nResults using scipy.optimize:")
+print("\nResults using scipy.optimize: (With HF embedding)")
 print(f"FCI energy: {fci_energy:.8f}")
 print(f" HF energy: {mol.e_hf:.8f} (Classical)")
 print(f"VQE energy: {best:.8f} (UCCSD ansatz)")
 # print()
 # print("Optimized parameters:", params)
 
 
-full_ham = mol.hamiltonian("f")
+full_ham = mol.hamiltonian("f", oei=mol.oei, tei=mol.tei, constant=0.0)
 mol_fci_energy = mol.eigenvalues(full_ham)[0]
 
 print(f"\nFCI energy: {mol_fci_energy:.8f} (Full Hamiltonian)")

src/qibochem/ansatz/__init__.py

@@ -1,15 +1,12 @@
-from qibochem.ansatz.basis_rotation import (
-    basis_rotation_gates,
-    basis_rotation_layout,
-    givens_qr_decompose,
-    unitary,
-)
-from qibochem.ansatz.hardware_efficient import hea
-from qibochem.ansatz.hf_reference import bk_matrix, bk_matrix_power2, hf_circuit
+from qibochem.ansatz.basis_rotation import basis_rotation_gates
+from qibochem.ansatz.hardware_efficient import he_circuit
+from qibochem.ansatz.hf_reference import hf_circuit
 from qibochem.ansatz.ucc import (
-    expi_pauli,
     generate_excitations,
     mp2_amplitude,
     sort_excitations,
+    ucc_ansatz,
     ucc_circuit,
 )
+
+# TODO: Probably can move some of the functions, e.g. generate_excitations/sort_excitations to a new 'util.py'