Coupled cluster

About: Coupled cluster is a research topic. Over the lifetime, 6280 publications have been published within this topic receiving 301055 citations.

Ab-initio coupled-cluster study of 16O.

Abstract: We report converged results for the ground and excited states and matter density of {sup 16}O using realistic two-body nucleon-nucleon interactions and coupled-cluster methods and algorithms developed in quantum chemistry Most of the binding is obtained with the coupled-cluster singles and doubles approach Additional binding due to three-body clusters (triples) is minimal The coupled-cluster method with singles and doubles provides a good description of the matter density, charge radius, charge form factor, and excited states of a one-particle, one-hole nature, but it cannot describe the first-excited 0{sup +} state Incorporation of triples has no effect on the latter finding

Relativistic effects on electric properties of many‐electron systems in spin‐averaged Douglas–Kroll and Pauli approximations

Abstract: Relativistic effects and electron correlation effects on the dipole moments of the coinage metal hydrides are investigated and compared employing one‐component (scalar) relativistic approximations based on the mass–velocity and Darwin operator and, alternatively, the Douglas–Kroll‐transformed spin‐averaged no‐pair Hamiltonian. The former of the two operators is found to perform quite accurately for CuH and AgH. For AuH the limits of the Pauli approximation seem to be reached, as can be inferred from a comparison with the values obtained within the spin‐averaged Douglas–Kroll no‐pair formalism. The coupled cluster calculations in the Douglas–Kroll no‐pair approximation for relativistic effects establish the dipole moment values of the coinage metal hydrides as equal to 1.05 a.u. for CuH, 1.14 a.u. for AgH and 0.52 for AuH. The corresponding non‐relativistic results are 1.14 a.u., 1.36 a.u., and 1.22 a.u., respectively. Some formal problems arising in applications of the Douglas–Kroll no‐pair approximation ...

Thermodynamic Properties of Molecular Borane Phosphines, Alane Amines, and Phosphine Alanes and the [BH4-][PH4+], [AlH4-][NH4+], and [AlH4-][PH4+] Salts for Chemical Hydrogen Storage Systems from ab Initio Electronic Structure Theory

Abstract: The heats of formation for the molecules BH3PH3, BH2PH2, HBPH, AlH3NH3, AlH2NH2, HAlNH, AlH3PH3, AlH2PH2, HAlPH, AlH4-, PH3, PH4, and PH4+, as well as the diatomics BP, AlN, and AlP, have been calculated by using ab initio molecular orbital theory. The coupled cluster with single and double excitations and perturbative triples method (CCSD(T)) was employed for the total valence electronic energies. Correlation consistent basis sets were used, up through the augmented quadruple-ζ, to extrapolate to the complete basis set limit. Additional d core functions were used for Al and P. Core/valence, scalar relativistic, and spin−orbit corrections were included in an additive fashion to predict the atomization energies. Geometries were calculated at the CCSD(T) level up through at least aug-cc-pVTZ and frequencies were calculated at the CCSD(T)/aug-cc-pVDZ level. The heats of formation of the salts [BH4-][PH4+](s), [AlH4-][NH4+](s), and [AlH4-][PH4+](s) have been estimated by using an empirical expression for the ...

Accurate calculation of anharmonic vibrational frequencies of medium sized molecules using local coupled cluster methods.

Abstract: Local coupled cluster methods were applied for the automated generation of accurate multidimensional potential energy surfaces for a set of test molecules ranging from six to nine atoms. Based on these surfaces anharmonic fundamental frequencies were computed using vibrational self-consistent field and configuration interaction methods. The computed vibrational frequencies are compared to those obtained from similar calculations using conventional coupled cluster methods and to experimental values. The results from local and conventional methods are found to be of similar accuracy and in close agreement with experimental values. In addition, an efficient parallelization of the fully automated surface generation code is presented.

The orbital-specific virtual local triples correction: OSV-L(T)

Abstract: A local method based on orbital specific virtuals (OSVs) for calculating the perturbative triples correction in local coupled cluster calculations is presented. In contrast to the previous approach based on projected atomic orbitals (PAOs), described by Schutz [J. Chem. Phys. 113, 9986 (2000)]10.1063/1.1323265, the new scheme works without any ad hoc truncations of the virtual space to domains. A single threshold defines the pair and triple specific virtual spaces completely and automatically. It is demonstrated that the computational cost of the method scales linearly with molecular size. Employing the recommended threshold a similar fraction of the correlation energy is recovered as with the original PAO method at a somewhat lower cost. A benchmark for 52 reactions demonstrates that for reaction energies the intrinsic accuracy of the coupled cluster with singles and doubles excitations and a perturbative treatment of triples excitations method can be reached by OSV-local coupled cluster theory with singles and doubles and perturbative triples, provided a MP2 correction is applied that accounts for basis set incompleteness errors as well as for remaining domain errors. As an application example the interaction energies of the guanine-cytosine dimers in the Watson-Crick and stacked arrangements are investigated at the level of local coupled cluster theory with singles and doubles and perturbative triples. Based on these calculations we propose new complete-basis-set-limit estimates for these interaction energies at this level of theory.