Dear ALPS users,
I am trying to use the sparsediag application to solve the standard Heisenberg Hamiltonian for various geometries.
So far I could however not figure out which Hamiltonian is actually implemented in the model "spin". Is it J*S1*S2, 2J*S1*S2 or 0.5J*S1*S2 ? Generally it would be good to know where in the code the model Hamiltonians can be found.
My second question is about boundary conditions. First I tried the "chain lattice" and varied the boundary conditions with the keyword "boundary" set to "open" or "closed" respectively, which had no effect on the determined eigenvalues. Is there a difference between using "open chain lattice" and "chain lattice" with "boundary" set to "open" ? I presume the reason for my problems is a simple user error, hence some help would be appreciated.
Best regards, Daniel