Periodic boundary conditions

[HumpyBlumpy]

Hello,

I was reading the Symbolic-Sums-and-Indices section of the docs, but I could not find there whether I can define a model on a lattice with periodic boundary conditions.
For example, for a simple tight-binding model, I wanted to to do something like that
ham = ∑(a(j)*a(j+1)',j)+∑(a(j)'*a(j+1),j)
This does not work. Is there another way of achieving this?

[ChristophHotter]

Sorry for the late reply.
Currently, it is not possible to write a Hamiltonian with shifted indices.
You can define a Hamiltonian with a double-sum as e.g. in the cavity antiresonance example. This includes all coupling terms, you can then just set the unnecessary ones to zero.