def get_fc(u):
fc = fermionchain.Spinful_Fermionic_Chain(n) # create the chain
h = 0
for i in range(n - 1):
h = h + fc.Cdagup[i] * fc.Cup[i + 1]
h = h + fc.Cdagdn[i] * fc.Cdn[i + 1]
for i in range(n):
h = h + u * (fc.Nup[i] - 0.5) * (fc.Ndn[i] - 0.5)
h = h + h.get_dagger()
fc.set_hamiltonian(h)
# Compute the dynamical correlator defined by
# <0|c_i^dagger \delta(H-E_0-\omega) c_j |0>
fc.nsweeps = 6
fc.maxm = 20 # maximum bond dimension in KPM
return fc
# Add the root path of the dmrgpy library
import os
import sys
sys.path.append(os.getcwd() + '/../../src')
# for example PATH = /home/jose/programs/dmrgpy/src
#PATH = PATH_TO_DMRGPY_LIBRARY
import numpy as np
import matplotlib.pyplot as plt
from dmrgpy import fermionchain
from dmrgpy import spinchain
n = 6 # number of spin sites
# first let us create a Hubabrd model
fc = fermionchain.Spinful_Fermionic_Chain(n) # create the object
fc.maxm = 20
U = 6.0
def ft(i, j):
if abs(i // 2 - j // 2) == 1 and i % 2 == j % 2:
return 1.0 # first neighbor coupling
if i == j: return -2 * U # set to half filling
return 0.0
def fu(i, j):
if i == j: return U
return 0.0
# Add the root path of the dmrgpy library
import os ; import sys ; sys.path.append(os.getcwd()+'/../../src')
import numpy as np
import matplotlib.pyplot as plt
from dmrgpy import fermionchain
n = 4
fc = fermionchain.Spinful_Fermionic_Chain(n//2) # create the chain
m = np.matrix(np.random.random((n,n)) + 1j*np.random.random((n,n)))
m = m + m.H # Make it Hermitian
def ft(i,j):
return m[i,j]
def fu(i,j):
if abs(i-j)==1: return 1.0
else: return 0.0
# Initialize the Hamiltonian
fc.set_hoppings(ft) # hoppings
fc.set_hubbard(fu) # hoppings
fc.set_swave_pairing(lambda i: 0.2)
e0 = fc.gs_energy(mode="ED") # energy with exact diagonalization
e1 = fc.gs_energy(mode="DMRG") # energy with DMRG
print("Energy with ED",e0)
print("Energy with DMRG",e1)
### Compute the dyamical correlator ###
