E_{CCSD(T)} = E_{CCSD} + E^{(4)}_{DT} + E^{(5)}_{ST} |
(10.12) |

which includes the following two terms:

E^{(4)}_{DT} |
= | t_{μ2}^{CCSD}〈μ_{2}|[H, T_{3}^{(2)}]| HF〉 |
(10.13) |

E^{(5)}_{ST} |
= | t_{μ1}^{CCSD}〈μ_{2}|[H, T_{3}^{(2)}]| HF〉 |
(10.14) |

where the approximate triples amplitudes evaluated as:

t^{(2)}_{aibjck} = - |
(10.15) |

In the literature one also finds sometimes the approximate triples model CCSD[T] (also denoted as CCSD+T(CCSD)), which is obtained by adding only