We
introduce perturbation and coupled-cluster theories based on
a cluster mean-field reference for describing the ground state of
strongly correlated spin systems. In cluster mean-field, the ground
state wave function is written as a simple tensor product of optimized
cluster states. The cluster language and the mean-field nature of
the ansatz allow for a straightforward improvement which uses perturbation
theory and coupled-cluster to account for intercluster correlations.
We present benchmark calculations on the 1D chain and 2D square J
1–J
2 Heisenberg
model, using cluster mean-field, perturbation theory, and coupled-cluster.
We also present an extrapolation scheme that allows us to compute
thermodynamic limit energies accurately. Our results indicate that,
with sufficiently large clusters, the correlated methods (cPT2, cPT4,
and cCCSD) can provide a relatively accurate description of the Heisenberg
model in the regimes considered, which suggests that the methods presented
can be used for other strongly correlated systems. Some ways to improve
upon the methods presented in this work are discussed.