Tensor network states and specifically matrix-product states have proven to be a powerful tool for simulating ground states of strongly correlated spin models. Recently, they have also been applied to interacting fermionic problems, specifically in the context of quantum chemistry. A new freedom arising in such nonlocal fermionic systems is the choice of orbitals, it being far from clear what choice of fermionic orbitals to make. In this Letter, we propose a way to overcome this challenge. We suggest a method intertwining the optimization over matrix product states with suitable fermionic Gaussian mode transformations. The described algorithm generalizes basis changes in the spirit of the Hartree-Fock method to matrix-product states, and provides a black box tool for basis optimization in tensor network methods.

Dahlem Center for Complex Quantum Systems Freie Universität Berlin 14195 Berlin Germany

J Heyrovský Institute of Physical Chemistry Academy of Sciences of the Czech Republic 18223 Prague Czech Republic

Strongly Correlated Systems Lendület Research Group Wigner Research Centre for Physics Hungarian Academy of Sciences 1525 Budapest Hungary

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Numerical and Theoretical Aspects of the DMRG-TCC Method Exemplified by the Nitrogen Dimer