We know that one can obtain ground state iMPS through iDMRG or iTEBD if setting infinite boundary condition. I am wondering is it possible to compute spectrum in momentum space (for example single particle dispersion or spin excitation spectrum) from local operators and known ground state?
Actually, I am not sure the difference between infinite boundary with shift invariance and periodic boundary condition with thermodynamic limit.
See [1810.07006] Tangent-space methods for uniform matrix product states for an excellent review of tangent space methods for uniform infinite MPS, including computing excitations using a single mode approximation. In the thermodynamic limit, open and periodic boundary conditions are the same (up to some details like dealing with degenerate states, topological excitations, etc.).
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