create solvers and interface modules

Co-authored-by: Johanna Zijderveld

examples/tEnergyTest.ipynb

 %% Cell type:code id: tags:
 
 ``` python
 import numpy as np
 import matplotlib.pyplot as plt
 from codes import utils, model, interface, solvers, hf
 ```
 
 %% Cell type:code id: tags:
 
 ``` python
 U0 = 1
 nk = 100
 filling = 2
 
 hopp = np.kron(np.array([[0, 1], [0, 0]]), np.eye(2))
 tb_model = {(0,): hopp + hopp.T.conj(), (1,): hopp, (-1,): hopp.T.conj()}
 
 
 def model_U(U):
     int_model = {
         (0,): U * np.kron(np.ones((2, 2)), np.eye(2)),
     }
     return model.Model(tb_model=tb_model, int_model=int_model)
 
 
 model0 = model_U(U0)
 model0.vectors = [*model0.int_model.keys()]
 model0.random_guess(model0.vectors)
 model0.kgrid_evaluation(nk=100)
 ```
 
 %% Cell type:code id: tags:
 
 ``` python
 hamiltonians_0 = utils.kgrid_hamiltonian(
     nk=nk, hk=utils.model2hk(tb_model=tb_model), dim=1
 )
 
 
 def groundstate(U):
     tb_mf_k = interface.find_groundstate_ham(
         model_U(U),
         filling=filling,
         nk=nk,
         solver=solvers.rspace_solver,
         cost_function=solvers.real_space_cost,
         return_kspace=True,
     )
     vals, vecs = np.linalg.eigh(tb_mf_k)
     EF = utils.get_fermi_energy(vals, filling)
     densityMatrix = hf.density_matrix(vals, vecs, EF)
 
     return tb_mf_k - EF * np.eye(hamiltonians_0.shape[-1]), densityMatrix
 
 tb_mf0, densityMatrix0 = groundstate(U0)
 mf0 = tb_mf0 - hamiltonians_0
 
 
 @np.vectorize
 def mfRescaled(alpha, mf0=mf0):
     hamiltonian = hamiltonians_0 + mf0 * alpha
     vals, vecs = np.linalg.eigh(hamiltonian)
     EF = utils.get_fermi_energy(vals, filling)
     densityMatrix = hf.density_matrix(vals, vecs, EF)
     return hf.total_energy(tb_mf0, densityMatrix)
 ```
 
 %% Cell type:code id: tags:
 
 ``` python
 alphas = np.linspace(0.5, 1.5, 21)
-plt.plot(alphas, mfRescaled(alphas), label="MF groundstate from U=1")
+plt.plot(alphas, mfRescaled(alphas))
 plt.axvline(x=1, c="k", ls="--")
 plt.ylabel("Total Energy")
 plt.xlabel(r"$\alpha$")
 plt.legend()
 ```
 
 %% Output
 
     <matplotlib.legend.Legend at 0x123524050>
 
 
 %% Cell type:code id: tags:
 
 ``` python
 ```