Next nearest neighbor interaction in 2D DMRG

Question

Hi,
I am trying to do some calculation using 2D dmrg code in Itensor.
2D dmrg code in ITENSOR includes nearest neighbor spin interactions.
e.g;
for(auto bnd : lattice)
{
ampo += 0.5,"S+",bnd.s1,"S-",bnd.s2;
ampo += 0.5,"S-",bnd.s1,"S+",bnd.s2;
ampo += "Sz",bnd.s1,"Sz",bnd.s2;
}

Is there any way so that next nearest neighbor spin interaction can be included in 2D dmrg code for square lattice or triangular lattice?
Thanks,
Ajit

Answer 1

Hi Ajit,
You are in luck. We do have a function already for making the square lattice with next-neighbor bonds but it just wasn't well documented. Following your question, I just added it to the documentation here:
http://itensor.org/docs.cgi?vers=cppv3&page=classes/lattice_functions

We don't have a function for next-neighbor on the triangular lattice however. The codes for all of these lattice functions is meant to be straightforward with the hope that users would contribute additional ones we are missing. If you would consider contributing the triangular next-neighbor case that would be great if you have time.

The codes for these functions can be found in the files:
itensor/mps/lattice/square.h
itensor/mps/lattice/triangular.h

Best regards,
Miles