A second-order perturbative correction to the coupled-cluster singles and doubles method: CCSD(2)

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Abstract
Recently, we introduced a new ansatz for developing perturbative corrections to methods based on coupled-cluster theory. In this article we apply this ansatz to the coupled-cluster singles and doubles (CCSD) method, generating the CCSD(2) method. We use the CCSD(2) method to study the double dissociation of water and to calculate spectroscopic constants of first row diatomic molecules. As long as Hartree–Fock is a reasonable approximation, CCSD(2) works very well.