8 Cluster Perturbation Theory

Cluster Perturbation Theory (CPT) is a simple approximation scheme that applies to lattice models with local interactions, like the Hubbard model, or models where the local interaction is predominant. It proceeds by tiling the lattice into identical, finite-size clusters, solving these clusters exactly and treating the inter-cluster hopping terms at first order in strong-coupling perturbation theory. This review will focus on the kinematical aspects of CPT, in particular the periodization procedure, and on the practical implementation of CPT using an exact diagonalization solver for the cluster. Applications of CPT will be briefly reviewed. 8.