Coexistence and competition of on-site and intersite Coulomb interactions in Mott-molecular-dimers

• A detailed study of correlation effects in a Mott-molecular-dimer system.
• Analysis of exact solution of the Hubbard model as function of model parameters and temperature.
• Our theory provides a novel route to explain the double peak structure in specfic heat.

We reveal the interplay between on-site (U)(U) and intersite (V)(V) Coulomb interactions in the extended two-site Hubbard model. Due to its atomic-like form quantum correlations intrinsic to Mott-molecular-dimers are exactly computed. Our results for physical quantities such as double occupancy and specific heat are consistent with those obtained for the one-band Hubbard model, suggesting that a two-site dimer model is able to capture the essential thermodynamic properties of strongly interacting electron systems. It is noted that intersite Coulomb interactions promote the formation of doublons, which compete with the spin-singlet state induced by the on-site Coulomb repulsion. Our results are expected to be relevant for understanding electronic and thermodynamical properties of interacting electrons in systems with strongly coupled magnetic atoms.