I'm trying to run dmrg on a non-Hermitian Z3 system, defined below. The system has an exact solution for the ground state in the open bc case, and iTensor typically gets within about 1% of the correct energy. I can't seem to achieve better convergence by changing the sweep parameters (including noise), and furthermore the final energy seems to depend on the initial state used, again to margins of ~1%. The system has a real ground state energy, but the rest of the spectrum is complex. I suspect this is the cause of the problem, as the algorithm appears to truncate to real numbers at various stages.

Is there anything you can suggest to improve convergence? I was considering attempting to rewrite the various dmrg functions using Cplx instead of Real - would this be worthwhile?

```
auto sites = Z3(N);
auto ampo = AutoMPO(sites);
for(int j = 1; j < N; ++j){
ampo += -1.0, "Sig", j;
ampo += -1.0,"Tau",j,"TauDag",j+1;
}
ampo += -1.0, "Sig", N;
if (periodic_bcs)
ampo += -1.0,"Tau",N,"TauDag",1;
auto H = MPO(ampo);
```

Note: the system is a special case of https://arxiv.org/pdf/1612.02617.pdf