Connected quadruple excitations in the coupled cluster theory

Monika Agnieszka Musial (1) , Stanislaw Kucharski (2)

1 Institute of Chemistry
2 chemistry

The role of the connected quadruple excitations in the coupled cluster (CC) theory is discussed. The full inclusion of the T4 (Q) operator in addition to singles (S), doubles (D) and triples (T) defines CCSDTQ method which offers a very accurate computational tool applicable to small molecular systems. The efficient organization of the CC equations results in the quasilinear formulation of the CCSDTQ scheme. A wider range of applications can be ensured with the approximate variants of the CCSDTQ approach. Due to possible factorization of the lowest order quadruple contribution to the energy the noniterative scheme has been formulated which requires n7 scaling. Performance of the CCSDTQ method has been discussed on the basis of the results obtained for several small molecules in confrontation with the reference full configuration interaction data.

Mots clés: Physical Sciences

Monika Agnieszka Musial, Stanislaw Kucharski. Connected quadruple excitations in the coupled cluster theory. Molecular Physics, 2010, 108 (21-23), pp.3235-3245. ⟨10.1080/00268976.2010.523523⟩. ⟨hal-00634687⟩