Topic
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 paper, a composite approach based on coupled cluster theory was used to predict the atomization energies and equilibrium structures of 13 small, first-row compounds, and the composite approach was found to yield a mean absolute deviation of 0.19
Abstract: A flexible, high-level, composite approach based on coupled cluster theory has been used to predict the atomization energies and equilibrium structures of 13 small, first-row compounds. Each of the major components in this approach can be systematically improved, thereby providing a practical measure of the inherent uncertainty (or degree of convergence) in the final results. Comparison with Active Thermochemical Table data, which relies on a network of experimental and theoretical data, showed excellent agreement for the atomization energies. With the addition of the latest molecular systems to the Computational Results Database, the composite approach was found to yield a mean absolute deviation of 0.19 kcal mol−1 and a root-mean-square deviation of 0.31 kcal mol−1 across 142 comparisons. If the analysis is limited to experimental data with estimated uncertainties of 0.2 kcal mol−1 or less, the error metrics are cut in half. Similar good agreement is found with experimental structures, but the relative ...
155 citations
TL;DR: In this article, the CCSDT-3 and CC3 parametrizations of the neutral ground state were used to obtain the vertical ionization potentials for N2, CO, and F2 with the most theoretically complete approximations.
Abstract: Vertical ionization potentials can be obtained from existing computer programs for the high-level treatment of excited states by simply including a continuum orbital in the basis set. Exploiting this feature easily allows final state energies for ionized states to be calculated at several previously untested levels of theory that go beyond the equation-of-motion coupled-cluster singles and doubles model. Values obtained for N2, CO, and F2 with the most theoretically complete approximations studied here (those based on the CCSDT-3 and CC3 parametrizations of the neutral ground state) are in excellent agreement with experiment when a large basis set is used.
155 citations
TL;DR: This work derives and compute effective valence-space shell-model interactions from ab initio coupled-cluster theory and applies them to open-shell and neutron-rich oxygen and carbon isotopes and finds good agreement between these results and those obtained from standard single-reference coupled-Cluster calculations for up to eight valence neutrons.
Abstract: We derive and compute effective valence-space shell-model interactions from ab initio coupled-cluster theory and apply them to open-shell and neutron-rich oxygen and carbon isotopes. Our shell-model interactions are based on nucleon-nucleon and three-nucleon forces from chiral effective-field theory. We compute the energies of ground and low-lying states, and find good agreement with experiment. In particular, our computed ${2}^{+}$ states are consistent with $N=14,16$ shell closures in $^{22,24}\mathrm{O}$, and a weaker $N=14$ shell closure in $^{20}\mathrm{C}$. We find good agreement between our coupled-cluster effective-interaction results with those obtained from standard single-reference coupled-cluster calculations for up to eight valence neutrons.
154 citations
TL;DR: In this paper, the nuclear magnetic shielding tensor functions for H2, HF, N2, CO, and F2 are calculated at the coupled cluster singles and doubles level augmented by a perturbative correction for triple excitations [CCSD(T)].
Abstract: Nuclear magnetic shielding tensor functions for H2, HF, N2, CO, and F2 are calculated at the coupled‐cluster singles and doubles level augmented by a perturbative correction for triple excitations [CCSD(T)]. The shielding constants for the lowest rovibrational states of these diatomics are obtained by solving the rovibrational Schrodinger equation with the finite‐element method. For H, C, and F, absolute scales for the nuclear magnetic shielding constants have been obtained by combining computed diamagnetic shieldings with paramagnetic contributions deduced from measured spin‐rotation constants and calculated rovibrational corrections. Since the experimental spin‐rotation constants for N2 and CO are inaccurate, shielding scales for N and O based on coupled cluster calculations are probably the most accurate available.
154 citations
TL;DR: The CCSD approximation is implemented, which includes single and double virtual excitations in a self-consistent manner, incorporating therefore the effects of the Coulomb and Breit interactions to all orders in these excitations.
Abstract: The relativistic Fock-space coupled cluster method for the direct calculation of ionization potentials and excitation energies (including fine structure) is presented and applied to atomic Au and its ions. The no-pair Dirac-Coulomb-Breit Hamiltonian is taken as the starting point. The CCSD approximation is implemented (where CCSD indicates coupled cluster with single and double excitations), which includes single and double virtual excitations in a self-consistent manner, incorporating therefore the effects of the Coulomb and Breit interactions to all orders in these excitations. A rather large basis set (21s17p11d7f) of kinetically balanced Gaussian spinors is used to span the atomic orbitals. All calculated energies (ionization potential and electron affinity of Au, excitation energies of Au and ${\mathrm{Au}}^{+}$) agree with experiment to 0.1 eV or better, with an average error of 0.06 eV. Fine-structure splittings are accurate to better than 0.01 eV.
154 citations