123 research outputs found
Comparison of one-dimensional and quasi-one-dimensional Hubbard models from the variational two-electron reduced-density-matrix method
Minimizing the energy of an -electron system as a functional of a
two-electron reduced density matrix (2-RDM), constrained by necessary
-representability conditions (conditions for the 2-RDM to represent an
ensemble -electron quantum system), yields a rigorous lower bound to the
ground-state energy in contrast to variational wavefunction methods. We
characterize the performance of two sets of approximate constraints,
(2,2)-positivity (DQG) and approximate (2,3)-positivity (DQGT) conditions, at
capturing correlation in one-dimensional and quasi-one-dimensional (ladder)
Hubbard models. We find that, while both the DQG and DQGT conditions capture
both the weak and strong correlation limits, the more stringent DQGT conditions
improve the ground-state energies, the natural occupation numbers, the pair
correlation function, the effective hopping, and the connected (cumulant) part
of the 2-RDM. We observe that the DQGT conditions are effective at capturing
strong electron correlation effects in both one- and quasi-one-dimensional
lattices for both half filling and less-than-half filling
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