Applicability of the almost-linear coupled-cluster method to nondynamically correlated states

• Autorzy: Grabowski, I. , Jankowski, K. , Kowalski, K.
• Języki publikacji: EN

Abstrakty

EN

To study the reliability of the almost-linear coupled-cluster (AL-CC) approah when applied to the description of state disclosing nondynamical correlation (or quasidegeneracy) effects, calculation have been performed for several systems widely used in quantum-chemical model calculations for quasidegenerate states (H4 (MBS),H2O (DZ), BeH2 (DZ), BH (DZP)). The AL-CC approach represents a special application of the recently formulated splitamplitude strategy for aproximating the equations of the CC methods (Chem. Phys.Lett., 256,141 (1996)) which consist in splitting the individual cluster amplitudes into two components - one of fixed value and the other determined from a set of modified CC equations. The linearization of the latter set yields the equations of the AL-CC method. In the present study the cluster operator is presented in terms of one- and two-body operators (AL-CCSD). The energies calculated are free from the singular behavior of their counterparts obtained for some strongly quasidegenerate states when using the standard linearized CC methods (L-CCSD). Outside the very strong quasidegeneracy region the AL-CCSD energies are very close to the CCSD ones, which demonstrate the usefulness of the low cost AL-CC approach.

Słowa kluczowe

EN

couples-cluster; nondynamical correlation; quasidegenerate state; almost-linear approach

• Czasopismo: Polish Journal of Chemistry
• Rocznik: 1998
• Tom: Vol. 72, nr 7S
• Strony: 1411-1420
• Opis fizyczny: Bibliogr. 22 poz., tab.

Twórcy

autor

Grabowski, I.

autor

Jankowski, K.

autor

Kowalski, K.

• Institute of Physics Nicholas Copernicus University 87-100 Toruń Poland