def plot_model(model_params, phi_ext=0.1):
model_params['phi_ext'] = phi_ext
M = BosonicHaldaneModel(model_params)
import matplotlib.pyplot as plt
plt.figure()
ax = plt.gca()
M.lat.plot_sites(ax)
M.coupling_terms['t1 Bd_i B_j'].plot_coupling_terms(ax, M.lat)
M.coupling_terms['t2 Bd_i B_j'].plot_coupling_terms(
ax, M.lat, text='{op_j!s} {strength_angle:.2f}', text_pos=0.9)
print(M.coupling_terms['t1 Bd_i B_j'].to_TermList())
ax.set_aspect(1.)
plt.show()
def run(model_params, phi_ext=np.linspace(0, 2.0, 7)):
data = dict(phi_ext=phi_ext, QL=[], ent_spectrum=[])
dmrg_params = {
'mixer': True, # setting this to True helps to escape local minima
'mixer_params': {
'amplitude': 1.e-5,
'decay': 1.2,
'disable_after': 30
},
'trunc_params': {
'svd_min': 1.e-10,
},
'lanczos_params': {
'N_min': 5,
'N_max': 20
},
'chi_list': {
0: 9,
10: 49,
20: 100
},
'max_E_err': 1.e-10,
'max_S_err': 1.e-6,
'max_sweeps': 150,
'verbose': 1.,
}
prod_state = [1]
if 2 * model_params['Lx'] * model_params['Ly'] % 4 != 0:
warnings.warn(
"Total filling factor = 1/4 cannot be achieved with this unit cell geometry."
)
for i in range(1, 2 * model_params['Lx'] * model_params['Ly']):
if i % 4 == 0:
prod_state.append(1)
else:
prod_state.append(0)
print(prod_state)
eng = None
for phi in phi_ext:
print("=" * 100)
print("phi_ext = ", phi)
model_params['phi_ext'] = phi
if eng is None: # first time in the loop
M = BosonicHaldaneModel(model_params)
psi = MPS.from_product_state(M.lat.mps_sites(),
prod_state,
bc=M.lat.bc_MPS)
eng = dmrg.TwoSiteDMRGEngine(psi, M, dmrg_params)
else:
del eng.engine_params['chi_list']
M = BosonicHaldaneModel(model_params)
eng.init_env(model=M)
E, psi = eng.run()
data['QL'].append(psi.average_charge(bond=0)[0])
data['ent_spectrum'].append(
psi.entanglement_spectrum(by_charge=True)[0])
return data