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Coupled cluster
About: Coupled cluster is a research topic. Over the lifetime, 6280 publications have been published within this topic receiving 301055 citations.
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TL;DR: In this article, the quartic force field of formaldehyde has been computed using large basis sets and augmented coupled cluster methods, which leads to fundamentals in very good agreement with experiment; the largest error (in [nu][sub 1]) is 7 cm[sup [minus]1].
115 citations
TL;DR: The elements of coupled-cluster theory that distinguish it from other ways of treating the correlation problem are presented in this article, where the elements of Coupled-Cluster (CC) theory are presented.
Abstract: The elements of coupled-cluster (CC) theory that distinguish it from other ways of treating the correlation problem are presented. These essential components required that new theory be developed to treat analytical gradients, excited states, higher order properties, and now multi-reference CC. Aided by these developments, CC theory provides the best answers for the largest number of problems in molecular structure and spectra. Many scientists who spent time at the Quantum Theory Project were instrumental in these developments.
115 citations
TL;DR: In this article, the authors calculated the heats of formation of NH3, NH2, NH and N at high levels of ab initio molecular orbital theory at 0 K using coupled cluster theory, including a perturbative treatment of the connected triple excitations.
Abstract: The heats of formation of NH3, NH2, NH and the ionization energies of NH3, NH2, NH, and N have been calculated at high levels of ab initio molecular orbital theory at 0 K. Geometries and frequencies were calculated with coupled cluster theory, including a perturbative treatment of the connected triple excitations and with correlation consistent basis sets up through augmented sextuple zeta in quality. Subsequent extrapolation of the total energies to the complete one-particle basis set limit was performed to further reduce the basis set truncation error. Additional improvements in the atomization energy were achieved by applying corrections for core/valence correlation, scalar relativistic, spin–orbit, and higher order correlation effects. Zero point energies were taken from anharmonic force fields where available or are based on appropriately scaled values. Using the R/UCCSD(T) method, we find the following heats of formation (kcal/mol) at 0 K: ΔHf(NH3)=−9.10±0.17 (calc.) versus −9.30±0.10 (expt.); ΔHf(N...
115 citations
TL;DR: CCSDR(3) calculations of vertical excitation energies are reported for a set of 24 molecules and 121 excited valence singlet states from a recently published benchmark of organic molecules, finding it to be a very cost-effective accurate alternative to CC3.
Abstract: CCSDR(3) calculations of vertical excitation energies are reported for a set of 24 molecules and 121 excited valence singlet states from a recently published benchmark of organic molecules. The same geometries (MP2/6−31G*) and basis set (TZVP) were employed as in our previous linear response CC2, CCSD, and CC3 calculations. The CCSDR(3) results are compared against the CCSD and CC3 results. Statistical evaluation of all CCSDR(3) excitation energies gives mean absolute deviations of 0.09 eV from CC3 and 0.30 eV from CCSD. For excited states, which are dominated by single excitations, the absolute mean deviation from CC3 is reduced to 0.02 eV and the maximum deviation is 0.09 eV. CCSDR(3) is thus a very cost-effective accurate alternative to CC3.
115 citations