## Abstract

A diagnostic for perturbation theory calculations, L_{2}, is defined and numerical results compared to the established L_{1} diagnostic from coupled-cluster theory. L_{2} is the lowest-order non-zero contribution to a Møller-Plesset perturbation expansion of T_{1}. L_{2} is a reasonable estimate of the importance of non-dynamical electron correlation, although not as reliable as T_{1}. L_{2} values ≤0.012 suggest that low orders of perturbation theory should yield reasonable results; L_{2} values between 0.012 and 0.015 suggest that caution is required in interpreting results from low orders of perturbation theory; L_{2} values ≥0.015 indicate that low orders of perturbation theory are not reliable for accurate results. Although not required mathematically, L_{2} is always less than T_{1} for the examples studied here.

Original language | English |
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Pages (from-to) | 402-408 |

Number of pages | 7 |

Journal | Chemical Physics Letters |

Volume | 243 |

Issue number | 5-6 |

DOIs | |

Publication status | Published - 22 Sept 1995 |

Externally published | Yes |

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