def get_fc(u):
fc = fermionchain.Fermionic_Hamiltonian(n) # create the chain
####### Input matrices #######
# Array with the hoppings and with hubbard couplings
# These are the matrices that you have to modify
hopping = np.zeros((n, n))
hubbard = np.zeros((n, n))
for i in range(n - 1):
hopping[i, i + 1] = 1.
hopping[i + 1, i] = 1.
for i in range(n):
U = u
hubbard[i, i] = U / 2.
hopping[i, i] = -U
# The implemented Hamiltonian is
# H = \sum_ij hopping[i,j] c^dagger_i c_j + hubbard[i,j] n_i n_j
# with n_i = c^\dagger_{i,up} c_{i,up} + c^\dagger_{i,dn} c_{i,dn}
# the previous matrices are for a half filled Hubbard chain
##############################
# Setup the Many Body Hamiltonian
fc.set_hoppings(lambda i, j: hopping[i, j]) # set the hoppings
fc.set_hubbard(lambda i, j: hubbard[i, j]) # set the hubbard constants
#fc.set_fields(lambda i: [0.,0.,0.2]) # set the hubbard constants
#fc.nsweeps = 7
# Compute the dynamical correlator defined by
# <0|c_i^dagger \delta(H-E_0-\omega) c_j |0>
i = 0 # first index of the dynamical correlator
j = 0 # second index of the dynamical correlator
delta = 0.1 # energy resolution (approximate)
fc.nsweeps = 6
fc.kpmmaxm = 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')
import numpy as np
import matplotlib.pyplot as plt
import fermionchain
n = 10
sc = fermionchain.Fermionic_Hamiltonian(n) # create the chain
def ft(i, j):
# if i==j: return 1.0
if abs(j - i) == 1: return 1.0 #+ np.random.random()
if i == j: return np.random.random()
# if i==j: return 1.1
return 0.0
sc.set_hoppings(ft) # hoppings
import time
#e0 = sc.gs_energy() # compute ground state energy with DMRG
e1 = sc.gs_energy_free() # compute ground state energy for free electrons
print("Free", e1)
sc.nsweeps = 1
es = [] # empty list
wf0 = None # no initial wavefunction
for i in range(10):
sc.nsweeps = 1 # do nothing
e = sc.gs_energy(wf0=sc.wf0)