Periodicity of domain walls for ferromagnetic ground state?

Question

Dear forum,
I am working with a 1D chain of 100 spin 1/2 particles at "half-filling". The model Hamiltonian contains (a) NN interactions and hopping that can be different between odd and even connections, and (b) NNN hopping and interaction. The only symmetry in this model is Ising symmetry: \sum_j < S^z _j > = 0. I am looking into a regime that is deeply ferromagnetic (FM) for all NN and NNN pairs, therefore, analytically one should expect 50 spins up, a domain wall, and 50 spins down, or the other way around (i.e., doubly degenerate ground state). However, DMRG gives a FM phase with several periodically distributed domain walls even though there is nothing in the Hamiltonian that would induce this periodicity. I am just wondering if DMRG is known to introduce such a periodicity through the way sweeping is done. Please let me know.

Thanks,
Niraj

Answer 1

The periodicity was dependent on the initial wavefunction MPS which was set to be the Neel state (10101010...) by default to keep the total Sz quantum number zero. When the DMRG code was implemented by randomly shuffling the positions of 1's and 0's in the initial wavefunction, still keeping the total Sz quantum number zero, the periodicity disappeared.