I want to calculate bipartite entanglement on a spin chain, governed by some interaction Hamiltonian. For this, I need the bipartite density matrix of any two sites on the spin chain. I know neighbouring two-site Wave functions are determined using the following:
ITensor bondket = psi.A(j)*psi.A(j+1);
But I want something like: ITensor bondket = psi.A(j)*psi.A(j+n); where, n=1,2,3,....
Can anyone tell how to do it?
Thanks in Advance.