The second-order reduced density matrix method and the two-dimensional Hubbard model

The second-order reduced density matrix method (the RDM method) has performed well in determining energies and properties of atomic and molecular systems, achieving coupled-cluster singles and doubles with perturbative triples (CCSD (T)) accuracy without using the wave-function. One question that arises is how well does the RDM method perform with the same conditions that result in CCSD (T) accuracy in the strong correlation limit. The simplest and a theoretically important model for strongly correlated electronic systems is the Hubbard model. In this paper, we establish the utility of the RDM method when employing the P,Q,G,T1 and T2′ conditions in the two-dimensional Hubbard model case and we conduct a thorough study applying the 4 × 4 Hubbard model employing a coefficients. Within the Hubbard Hamiltonian we found that even in the intermediate setting, where U/t is between 4 and 10, the P, Q, G, T1 and T2′ conditions reproduced good ground state energies.