Investigation of a diagnostic for perturbation theory. Comparison to the T1 diagnostic of coupled-cluster theory

Timothy J. Lee, Martin Head-Gordon, Alistair P. Rendell

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25 Citations (Scopus)


A diagnostic for perturbation theory calculations, L2, is defined and numerical results compared to the established L1 diagnostic from coupled-cluster theory. L2 is the lowest-order non-zero contribution to a Møller-Plesset perturbation expansion of T1. L2 is a reasonable estimate of the importance of non-dynamical electron correlation, although not as reliable as T1. L2 values ≤0.012 suggest that low orders of perturbation theory should yield reasonable results; L2 values between 0.012 and 0.015 suggest that caution is required in interpreting results from low orders of perturbation theory; L2 values ≥0.015 indicate that low orders of perturbation theory are not reliable for accurate results. Although not required mathematically, L2 is always less than T1 for the examples studied here.

Original languageEnglish
Pages (from-to)402-408
Number of pages7
JournalChemical Physics Letters
Issue number5-6
Publication statusPublished - 22 Sep 1995
Externally publishedYes


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