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This paper extends previous work on the cluster mean field (cMF) wavefunction by analyzing the convergence of cluster perturbation theory (cPT) and coupled cluster (cCC) methods, specifically cPT7 and cCCSDTQ5, for the J1-J2 Heisenberg model in the thermodynamic limit. The authors demonstrate that the energy converges with these higher-order methods, confirming the effectiveness of cMF in transforming strongly correlated systems into weakly correlated ones suitable for perturbative approaches. Additionally, they provide insights into efficient cluster-based calculations, which are essential for handling the increased computational demands of these advanced techniques.
Energy convergence in higher-order cluster methods confirms the utility of cluster mean field theory for strongly correlated systems, unlocking new computational efficiencies.
In previous work, it was shown that using the cluster mean field(cMF) wavefunction as the zeroth order wavefunction for perturbation theory and coupled cluster produces a reasonable approximation for the J 1-J 2 Heisenberg model in the thermodynamic limit(TDL). However, this work was limited to cPT4 and cCCSD. The central claim of cMF is that it takes strongly correlated systems and makes them weakly correlated so that PT weakly correlated methods can be used. To confirm that this claim is true, it is important to show that the PT and CC series converge. In this paper, we extend the previous calculations to cPT7 and cCCSDTQ5 where we show that the energy is converging. We also discuss how to perform cluster based calculations efficiently in the thermodynamic limit, which is crucial for these more expensive calculations.