Exact Diagonalization Study of an Extended Hubbard Model for a Cubic Cluster at Quarter Filling

TL;DR

This study uses exact diagonalization to analyze the thermodynamics of a cubic 8-site Hubbard model at quarter filling, focusing on specific heat and magnetic susceptibility influenced by extended interactions.

Contribution

It provides a detailed analysis of how second nearest-neighbor hopping and Coulomb interactions affect thermodynamic responses in a finite Hubbard cluster.

Findings

Second nearest-neighbor hopping significantly influences temperature-dependent response functions.

Coulomb interactions between nearest neighbors alter thermodynamic behavior.

Schottky model predictions are compared with full spectrum calculations.

Abstract

In the paper the thermodynamics of a cubic cluster with 8 sites at quarter filling is characterized by means of exact diagonalization technique. Particular emphasis is put on the behaviour of such response functions as specific heat and magnetic susceptibility. The system is modelled with extended Hubbard model which includes electron hopping between both first and second nearest neighbours as well as coulombic interactions, both on-site and between nearest-neighbour sites. The importance of hopping between second nearest neighbours and coulombic interactions between nearest neighbours for the temperature dependences of thermodynamic response functions is analysed. In particular, the predictions of Schottky model are compared with the calculations based on the full energy spectrum.