Coupled cluster

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

A comparison of techniques for predicting higher order correlation effects: Diatomic dissociation energies

Abstract: The impact of higher-order correlation effects on dissociation energies was measured for three diatomic molecules (HF, N2, and CO) using standard coupled cluster theory, including a perturbative treatment of triple excitations, as the baseline for comparison. Among the higher-order methods examined were two variations of coupled cluster theory [CCSDT and CCSD(TQ)] and two approximations to full configuration interaction. Basis sets were chosen from the correlation-consistent family of basis sets, with the largest being the aug-cc-pVQZ set. Polarized valence double zeta quality basis sets were found to yield corrections that differed substantially from larger basis set results. At the double zeta level, higher order corrections increased the binding energies, whereas calculations with triple and quadruple zeta basis sets gave the opposite effect. Although the absolute magnitude of the higher-order corrections was small for these diatomics, they were nonetheless significant in light of a target accuracy of ...

Communication: Acceleration of coupled cluster singles and doubles via orbital-weighted least-squares tensor hypercontraction.

Abstract: We apply orbital-weighted least-squares tensor hypercontraction decomposition of the electron repulsion integrals to accelerate the coupled cluster singles and doubles (CCSD) method. Using accurate and flexible low-rank factorizations of the electron repulsion integral tensor, we are able to reduce the scaling of the most vexing particle-particle ladder term in CCSD from O(N6) to O(N5), with remarkably low error. Combined with a T1-transformed Hamiltonian, this leads to substantial practical accelerations against an optimized density-fitted CCSD implementation.

Correlation problems in atomic and molecular systems. VII. Application of the open‐shell coupled‐cluster approach to simple π‐electron model systems

Abstract: The coupled-cluster variational-like direct approach to the calculation of ionization and electron attachment energies and of excitation energies is applied to several π-electron model systems, using the PPP Hamiltonian with various parametrizations. A simple approximation, which represents the triexcited clusters in terms of disconnected W1T2 terms, is employed. All the necessary diagrams for both excitation energy and ionization potential (electron affinity) calculations are given in the compact Hugenholtz nonoriented form. The results of the calculations for benzene, trans-butadiene, all-trans-hexatriene, and fulvene are compared with the corresponding full CI results, and the conclusions about the validity and efficiency of this approach are drawn.

The linked singles and doubles model: An approximate theory of electron correlation based on the coupled-cluster ansatz

Abstract: From the diagrammatic construction of the full coupled‐cluster theory of all single and double excitations, a linearized theory, a direct configuration interaction theory (CISD), a CEPA‐like theory, and a linked singles and doubles (LSD) theory are separated. These theories are then compared with one another, with the results from full fourth‐order perturbation theory, and with exact results when available. The LSD model, corresponding to the removal of unlinked terms of the CISD, and its spin adapted version, appear most accurate in Pariser–Parr–Pople studies where the exact numbers are known. Examples within the localized bond model are given indicating that this model is also the most successful of those examined in generating not only the basis set correlation, but the necessary delocalization and polarization required to correct for the zeroth‐order local description.

On the performance of quantum chemical methods to predict solvatochromic effects: The case of acrolein in aqueous solution.

Abstract: The performance of the Hartree–Fock method and the three density functionals B3LYP, PBE0, and CAM-B3LYP is compared to results based on the coupled cluster singles and doubles model in predictions of the solvatochromic effects on the vertical n →* and →* electronic excitation energies of acrolein. All electronic structure methods employed the same solvent model, which is based on the combined quantum mechanics/molecular mechanics approach together with a dynamical averaging scheme. In addition to the predicted solvatochromic effects, we have also performed spectroscopic UV measurements of acrolein in vapor phase and aqueous solution. The gas-to-aqueous solution shift of the n →* excitation energy is well reproduced by using all density functional methods considered. However, the B3LYP and PBE0 functionals completely fail to describe the →* electronic transition in solution, whereas the recent CAM-B3LYP functional performs well also in this case. The →* excitation energy of acrolein in water solution is found to be very dependent on intermolecular induction and nonelectrostatic interactions. The computed excitation energies of acrolein in vacuum and solution compare well to experimental data. © 2008 American Institute of Physics. DOI: 10.1063/1.2918537