Constructing Low-Energy Effective Models for the Hydrogen Chain using sb-DMRG

Sliced-basis DMRG(sb-DMRG) is used to simulate a chain of hydrogen atoms which is then transformed to an effective low-energy model. The downfolding procedure involves a change of basis from the real-space grid of the hydrogen chain to a set of atom-centered Wannier functions. Instead of conventional Wannier functions constructed from mean-field bands, we construct them directly from the exact DMRG one particle density matrix. We consider two versions of this. In the first, we use only the ground state to construct the density matrix. This more conventional approach produces a model which poorly reproduces spin and charge gaps. We obtain much better models using Wannier functions constructed from an average density matrix over a small set of low lying DMRG eigenstates.