Coupled‐cluster method truncated at quadruples

The coupled‐cluster (CC) equations including single, double, triple, and quadruple excitation amplitudes (CCSDTQ) are derived diagramatically, and the complete set of CCSDTQ equations are presented. These equations have been programmed and an iterative reduced linear equation method is used to solve these equations. The potential curves for the dissociation of a model system with a single bond (Li2 and LiH) is calculated using CC doubles (CCD), singles and doubles (CCSD), singles, doubles, and triples (CCSDT), and CCSDTQ. These calculations demonstrate the magnitude of the CC contributions arising from single, double, triple, and quadruple excitation amplitudes to the stretching of a chemical bond.

[1]  J. Hubbard.  The description of collective motions in terms of many-body perturbation theory. II. The correlation energy of a free-electron gas , 1958, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[2]  F. Coester,et al.  Short-range correlations in nuclear wave functions , 1960 .

[3]  O. Sǐnanoğlu,et al.  MANY-ELECTRON THEORY OF ATOMS AND MOLECULES. I. SHELLS, ELECTRON PAIRS VS MANY-ELECTRON CORRELATIONS , 1962 .

[4]  J. Cizek.  On the Correlation Problem in Atomic and Molecular Systems. Calculation of Wavefunction Components in Ursell-Type Expansion Using Quantum-Field Theoretical Methods , 1966 .

[5]  R. Nesbet.  Atomic Bethe-Goldstone Equations. III. Correlation Energies of Ground States of Be, B, C, N, O, F, and Ne , 1968 .

[6]  Josef Paldus,et al.  Correlation problems in atomic and molecular systems. V. Spin‐adapted coupled cluster many‐electron theory , 1977 .

[7]  J. S. Binkley,et al.  Electron correlation theories and their application to the study of simple reaction potential surfaces , 1978 .

[8]  Kimihiko Hirao,et al.  Cluster expansion of the wavefunction. Symmetry-adapted-cluster expansion, its variational determination, and extension of open-shell orbital theory , 1978 .

[9]  Rodney J. Bartlett,et al.  Molecular Applications of Coupled Cluster and Many-Body Perturbation Methods , 1980 .

[10]  R. Bartlett.  Many-Body Perturbation Theory and Coupled Cluster Theory for Electron Correlation in Molecules , 1981 .

[11]  Rodney J. Bartlett,et al.  The reduced linear equation method in coupled cluster theory. , 1981 .

[12]  C. E. Dykstra,et al.  An electron pair operator approach to coupled cluster wave functions. Application to He2, Be2, and Mg2 and comparison with CEPA methods , 1981 .

[13]  R. Bartlett,et al.  A full coupled‐cluster singles and doubles model: The inclusion of disconnected triples , 1982 .

[14]  Ajit Banerjee,et al.  Applications of multiconfigurational coupled‐cluster theory , 1982 .

[15]  Sourav Pal,et al.  Use of a size-consistent energy functional in many electron theory for closed shells , 1983 .

[16]  W. Kutzelnigg,et al.  Quantum chemistry in Fock space. II. Effective Hamiltonians in Fock space , 1983 .

[17]  J. G. Zabolitzky,et al.  Atomic and molecular correlation energies with explicitly correlated Gaussian geminals. IV. A simplified treatment of strong orthogonality in MBPT and coupled cluster calculations , 1984 .

[18]  R. Bartlett,et al.  Erratum: A coupled cluster approach with triple excitations [J. Chem. Phys. 81, 5906 (1984)] , 1985 .

[19]  U. Kaldor,et al.  Open-shell coupled-cluster theory applied to atomic and molecular systems , 1985 .

[20]  Rodney J. Bartlett,et al.  Fifth-Order Many-Body Perturbation Theory and Its Relationship to Various Coupled-Cluster Approaches* , 1986 .

[21]  R. Bartlett,et al.  Optimized virtual orbital space for high‐level correlated calculations , 1987 .

[22]  R. Bartlett,et al.  The full CCSDT model for molecular electronic structure , 1987 .

[23]  R. Bartlett,et al.  Towards a full CCSDT model for electron correlation. CCSDT-n models , 1987 .

[24]  Henry F. Schaefer,et al.  A new implementation of the full CCSDT model for molecular electronic structure , 1988 .

[25]  Julia E. Rice,et al.  An efficient closed-shell singles and doubles coupled-cluster method , 1988 .

[26]  R. Bartlett,et al.  Coupled-cluster methods that include connected quadruple excitations, T4: CCSDTQ-1 and Q(CCSDT) , 1989 .

[27]  Nevin Horace Oliphant,et al.  A multireference coupled-cluster method using a single-reference formalism. , 1991 .