I calculate a simple tJ model ,however the energy is not convergent. The program and the result are below:`#include "itensor/all.h"
using namespace itensor;
int main()
{
int L = 80;
double t = 1.0;
double Jz = 1.0;
auto sites = tJ(L);
auto ampo = AutoMPO(sites);
for(int j = 1; j < L; ++j)
{
ampo += -t,"Cdagup",j,"Cup",j+1;
ampo += -t,"Cdagup",j+1,"Cup",j;
ampo += -t,"Cdagdn",j,"Cdn",j+1;
ampo += -t,"Cdagdn",j+1,"Cdn",j;
ampo += Jz,"Sz",j,"Sz",j+1;
}
auto H = toMPO(ampo);
auto state = InitState(sites);
for(int j = 1; j <= L; ++j)
{
if(j%4==1) state.set(j,"Up");
else if(j%4==2) state.set(j,"Dn");
}
auto psi0 = MPS(state);
auto sweeps = Sweeps(20);
sweeps.noise() = 1E-6,1E-6,1E-8,1E-10,1E-12;
sweeps.maxdim() = 20,50,100,200;
sweeps.cutoff() = 1E-14;
auto [energy,psi] = dmrg(H,psi0,sweeps,"Quiet");
return 0;
}`
Result:
vN Entropy at center bond b=40 = 4.331806189036
Eigs at center bond b=40: 0.0870 0.0848 0.0782 0.0761 0.0156 0.0150 0.0149 0.0142 0.0133 0.0128
Largest link dim during sweep 16/20 was 200
Largest truncation error: 5.56915e-06
Energy after sweep 16/20 is -50.801917299231
Sweep 16/20 CPU time = 27.42s (Wall time = 28.95s)
vN Entropy at center bond b=40 = 4.353591702822
Eigs at center bond b=40: 0.0883 0.0861 0.0764 0.0756 0.0149 0.0145 0.0144 0.0137 0.0126 0.0125
Largest link dim during sweep 17/20 was 200
Largest truncation error: 6.09279e-06
Energy after sweep 17/20 is -50.509784548999
Sweep 17/20 CPU time = 27.53s (Wall time = 28.85s)
vN Entropy at center bond b=40 = 4.370626565212
Eigs at center bond b=40: 0.0897 0.0870 0.0769 0.0731 0.0145 0.0145 0.0140 0.0131 0.0122 0.0119
Largest link dim during sweep 18/20 was 200
Largest truncation error: 6.65186e-06
Energy after sweep 18/20 is -50.664949183470
Sweep 18/20 CPU time = 27.84s (Wall time = 28.78s)
vN Entropy at center bond b=40 = 4.384005562025
Eigs at center bond b=40: 0.0920 0.0877 0.0747 0.0729 0.0144 0.0141 0.0136 0.0124 0.0115 0.0114
Largest link dim during sweep 19/20 was 200
Largest truncation error: 7.03868e-06
Energy after sweep 19/20 is -50.695774689683
Sweep 19/20 CPU time = 27.52s (Wall time = 28.37s)
vN Entropy at center bond b=40 = 4.393822650435
Eigs at center bond b=40: 0.0938 0.0887 0.0752 0.0701 0.0143 0.0137 0.0130 0.0117 0.0111 0.0108
Largest link dim during sweep 20/20 was 200
Largest truncation error: 7.32056e-06
Energy after sweep 20/20 is -50.292667154544
Sweep 20/20 CPU time = 27.61s (Wall time = 29.07s)