Physical Review B
Periodic cluster perturbation theory
Minh-Tien Tran
Abstract
A periodic cluster perturbation theory is used to investigate a fermion system. The theory is based on the dynamical cluster approximation with relaxing of self-consistency. Within the periodic cluster perturbation theory the self-energy is approximated by the self-energy of an isolated cluster with periodic boundary conditions. The small parameter of the theory is of order of $1∕{L}_{c}$, where ${L}_{c}$ is the linear size of the cluster. It is found that within the periodic cluster perturbation theory, quantities averaged over the cluster converge rapidly with corrections $O(1∕{L}_{c}^{2})$, whereas within the cluster perturbation theory, they converge with corrections $O(1∕{L}_{c})$.