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Triple excitation effects in coupled-cluster calculations of indirect spin–spin coupling constants (2001)

Auer, Alexander A. ; Gauss, Jürgen

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 115 (2001), S. 1619-1622

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The effect of triple excitations in coupled-cluster calculations of indirect spin-spin coupling constants is investigated in coupled-cluster singles and doubles (CCSD) calculations augmented by a perturbative treatment of triples [CCSD(T)], in calculations based on the CC3 model as well as in coupled-cluster singles, doubles, and triples (CCSDT) calculations. Though triple excitation effects are in most cases not particularly pronounced, it is demonstrated that among the approximate schemes for handling triples only the CC3 model with no orbital relaxation included (unrelaxed CC3) provides an adequate description. The otherwise successful CCSD(T) aproach appears to either significantly overestimate triple excitation effects or to yield corrections with the wrong sign in comparison to CCSDT. © 2001 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1386698

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Analytic gradients for the coupled-cluster singles, doubles, and triples (CCSDT) model (2002)

Gauss, Jürgen

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 116 (2002), S. 1773-1782

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The first implementation of analytic gradients for the coupled-cluster singles, doubles, triples (CCSDT) model is described. The relevant theoretical expressions are given in a diagrammatic form together with the corresponding algebraic formulas. The computational requirements of CCSDT gradient calculations are discussed and their applicability demonstrated by performing benchmark calculations for molecular geometries with large correlation-consistent basis sets. A statistical analysis of the data reveals that CCSDT and CCSD(T) in most cases perform equally well. The CCSDT calculations thus provide further evidence for the high accuracy of the CCSD(T) approach. © 2002 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1429244

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Analytic second derivatives for the full coupled-cluster singles, doubles, and triples model: Nuclear magnetic shielding constants for BH, HF, CO, N2, N2O, and O3 (2002)

Gauss, Jürgen

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 116 (2002), S. 4773-4776

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: An implementation of analytic second derivatives for the coupled-cluster singles, doubles, and triples (CCSDT) model is reported and applied to the calculation of nuclear magnetic shielding constants of BH, HF, CO, N2, N2O, and O3. The CCSDT calculations yield further evidence for the high accuracy provided by chemical shift calculations employing the coupled-cluster singles, doubles (CCSD) approach augmented by a perturbative triples correction [CCSD(T)]. © 2002 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1462612

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