def __init__(self, L=2, S=0.5, J=1., Delta=1., hz=0.):
spin = SpinSite(S=S, conserve="Sz")
# the lattice defines the geometry
lattice = Chain(L, spin, bc="open", bc_MPS="finite")
CouplingModel.__init__(self, lattice)
# add terms of the Hamiltonian
self.add_coupling(J * 0.5, 0, "Sp", 0, "Sm", 1) # Sp_i Sm_{i+1}
self.add_coupling(J * 0.5, 0, "Sp", 0, "Sm", -1) # Sp_i Sm_{i-1}
self.add_coupling(J * Delta, 0, "Sz", 0, "Sz", 1)
# (for site dependent prefactors, the strength can be an array)
self.add_onsite(-hz, 0, "Sz")
# finish initialization
# generate MPO for DMRG
MPOModel.__init__(self, lat, self.calc_H_MPO())
# generate H_bond for TEBD
NearestNeighborModel.__init__(self, lat, self.calc_H_bond())
def __init__(self, L=10, J=1, gamma=1, Y=0, hz=0, options={}):
# use predefined local Hilbert space and onsite operators
site = SpinSite(S=1 / 2, conserve=None)
self.L = L
lat = Chain(L, site, bc="open", bc_MPS="finite") # define geometry
MultiCouplingModel.__init__(self, lat)
# add terms of the Hamiltonian;
# operators "Sx", "Sy", "Sz" are defined by the SpinSite
self.add_coupling(J + gamma, 0, "Sx", 0, "Sx", 1)
self.add_coupling(J - gamma, 0, "Sy", 0, "Sy", 1)
self.add_multi_coupling(Y, [("Sx", -1, 0), ("Sz", 0, 0), ("Sy", 1, 0)])
self.add_multi_coupling(-Y, [("Sy", -1, 0), ("Sz", 0, 0),
("Sx", 1, 0)])
self.add_onsite(hz, 0, "Sz")
# finish initialization
MPOModel.__init__(self, lat, self.calc_H_MPO())
self.psi = MPS.from_product_state(self.lat.mps_sites(), [0] * L,
"finite")
self.options = options
self.dmrg_retval = None
def __init__(self, L=10, J=1, Y=0, hz=0, options={}):
# use predefined local Hilbert space and onsite operators
site = SpinSite(S=1, conserve=None)
self.L = L
lat = Chain(L, site, bc="open", bc_MPS="finite") # define geometry
MultiCouplingModel.__init__(self, lat)
# add terms of the Hamiltonian;
# operators "Sx", "Sy", "Sz" are defined by the SpinSite
self.add_coupling(J, 0, "Sx", 0, "Sx", 1)
self.add_coupling(J, 0, "Sy", 0, "Sy", 1)
self.add_coupling(J, 0, "Sz", 0, "Sz", 1)
for oper1 in ['Sx', 'Sy', 'Sz']:
for oper2 in ['Sx', 'Sy',
'Sz']: # (\vec S(i) \cdot \vec S(i+1))^2 coupling
self.add_multi_coupling(Y, [(oper1, 0, 0),(oper2, 0, 0),\
(oper1, 1, 0),(oper2, 1, 0)] ) #note that there are two operators on one site
self.add_onsite(hz, 0, "Sz")
# finish initialization
MPOModel.__init__(self, lat, self.calc_H_MPO())
self.psi = MPS.from_product_state(self.lat.mps_sites(), [0] * L,
"finite")
self.options = options
self.dmrg_retval = None
def init_sites(self, model_params):
# conserve = get_parameter(model_params, 'conserve', None, self.name)
conserve = model_params.get('conserve', None)
S = model_params.get('S', 0.5)
fs = SpinSite(S=S, conserve=conserve)
return [fs, fs, fs, fs]