Hi all,

fist of all, I am using the version 1.2.

I am trying to compute the following quantity:

G*{ij}(t)= < 0 | e^{iHt} * a*i * e^{-iHt} * a^{\dagger}_j | 0 >

where | 0 > is the ground state of the Kitaev chain with Hamiltonian H, and a and a^{\dagger} are the usual fermionic operator. My idea is to compute the two time evolution of the two states separately:

- a^{\dagger}_j | 0 >
- |0>

in order to obtain:

- e^{-iHt} * a^{\dagger}_j | 0 >
- e^{-iHt} | 0 >.

Then I apply the operator a^{\dagger}*i on the second state in order to obtain the state a{\dagger}*i * e^{-iHt} | 0 >. Finally, I would like to take the bra - ket product between this two states for computing the previous quantity G_ij(t).

I attach the code:

```
auto sites = Spinless(N,{"ConserveNf",false});
auto ampo = AutoMPO(sites);
for(int i=1; i<N; ++i) {
ampo += -1.0*w, "Cdag", i, "C", i+1;
ampo += -1.0*w, "Cdag", i+1, "C", i;
ampo += +1.0*delta, "C", i, "C", i+1;
ampo += +1.0*std::conj(delta), "Cdag", i+1,"Cdag", i;
ampo += +1.0*Uint, "Nint", i, "Nint", i+1;
}
for(int i = 1; i <= N; ++i) {
ampo += -1.0*mu, "N", i;
}
auto H = IQMPO(ampo);
auto state = InitState(sites);
auto psi = IQMPS(state);
auto energy = dmrg(psi,H,sweeps,{"Quiet",true});
// Print the final energy reported by DMRG
printfln("\nGround State Energy = %.10f \n\n", energy);
// Time Evolution
auto tau = 0.01;
auto expH = toExpH<IQTensor>(ampo,tau*Cplx_i);
auto args = Args("Cutoff=",1E-9,"Maxm=",3000);
auto ttotal = 3.0;
auto nt = int(ttotal/tau+(1e-9*(ttotal/tau)));
for(int n = 1; n <= nt; ++n) {
for(int i = 1; i <=N; ++i) {
for(int j = i; j <=N; ++j) {
if (j > i) {
auto op_i = sites.op("Cdag", i);
auto op_j = sites.op("Cdag", j);
// Creating the new MPS for the ket
auto psi_ket = psi;
psi_ket.position(j);
auto new_psi_ket = op_j*psi_ket.A(j);
new_psi_ket.noprime();
psi_ket.setA(j, new_psi_ket);
// Evolving the ket
psi_ket = exactApplyMPO<IQTensor>(expH,psi_ket,args);
normalize(psi_ket);
// Evolving the state for the bra
psi = exactApplyMPO<IQTensor>(expH,psi,args);
normalize(psi);
// Replace the operator CDag in the state for the bra
psi.position(i);
auto new_psi = op_i*psi_ket.A(i);
new_psi.noprime();
psi.setA(i, new_psi);
psi.position(1);
psi_ket.position(1);
auto result = overlapC(psi, psi_ket);
Print(result);
}
}
}
printfln("MPO: Time %d, Maximum MPS bond dimension after time evolution is %d", n*tau,maxM(psi));
}
```

The problem is that I obtain the following error:

From line 211, file /Users/giuseppe/Desktop/iTensor/ITensor/itensor/itensor_interface.ih

Wrong number of IndexVals passed to real/cplx (expected 2, got 0)

Wrong number of IndexVals passed to real/cplx (expected 2, got 0)

Any idea?

Thank you very much.