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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: Coupled Clustered Clustering (CCL) as discussed by the authors is a coupled cluster approach to the many-electron correlation problem for both closed and open shell systems.
Abstract: A brief overview concerning the motivations and the development of the coupled cluster approach to the many-electron correlation problem for both closed and open shell systems is given. The basic characteristics and applications of this approach are briefly summarized as well as its relationship to other approaches.
145 citations
TL;DR: In this article, the potential energy surface of the water trimer has been studied through the use of ab initio quantum mechanical methods and five stationary points were located, including one minimum and two transition states.
Abstract: The potential energy surface of the water trimer has been studied through the use of ab initio quantum mechanical methods. Five stationary points were located, including one minimum and two transition states. All geometries were optimized at levels up to the double-[Zeta] plus polarization plus diffuse (DZP + diff) single and double excitation coupled cluster (CCSD) level of theory. CCSD single energy points were obtained for the minimum, two transition states, and the water monomer using the triple-[Zeta] plus double polarization plus diffuse (TZ2P + diff) basis at the geometries predicted by the DZP + diff CCSD method. Reported are the following: geometrical parameters, total and relative energies, harmonic vibrational frequencies and infrared intensities for the minimum, and zero point vibrational energies for the minimum, two transition states, and three separated water molecules. 27 refs., 5 figs., 10 tabs.
144 citations
TL;DR: In this article, the authors used integral-direct coupled cluster (ICCSD) to estimate the CCSD(T) dissociation energy of the benzene-argon van der Waals complex.
Abstract: Equilibrium dissociation energies De of the benzene-argon van der Waals complex are calculated in the ground state S0 and in the excited state S1 using integral-direct coupled cluster methods. The results confirm previous investigations of S0, showing that high quality correlation consistent basis sets and connected triple excitations are imperative for a good description of the van der Waals complex. We estimate the CCSD(T) dissociation energy De=389±2 cm-1 for the ground state S0. Using the CCSD linear response approach the frequency shift (redshift) δve=19 cm-1 is obtained. Accurate spectroscopic structural data and frequency shifts δv0 for the 60 1 band of the S1←S0 transition are available for most of the benzene-rare gas atom complexes. However, the experimental determination of absolute dissociation energies of these complexes is connected with much larger uncertainties. The theoretical result agrees very well with the experimentally available redshift, showing that integral-direct coupled cluster methods will become an important tool in the study of van der Waals complexes in the future. © 1998 American Institute of Physics.
144 citations
TL;DR: A thorough comparative investigation of the excitation energies of the anionic and neutral forms of the green fluorescent protein (GFP) chromophore in the gas phase using a variety of first-principle theoretical approaches commonly used to access excited state properties of photoactive molecules finds that all approaches give roughly the same vertical excitation, while TDDFT predicts an excitation for the neutral Chromophore significantly lower than the highly correlated methods.
Abstract: We perform a thorough comparative investigation of the excitation energies of the anionic and neutral forms of the green fluorescent protein (GFP) chromophore in the gas phase using a variety of first-principle theoretical approaches commonly used to access excited state properties of photoactive molecules. These include time-dependent density functional theory (TDDFT), complete-active-space second-order perturbation theory (CASPT2), equation-of-motion coupled cluster (EOM-CC), and quantum Monte Carlo (QMC) methods. We find that all approaches give roughly the same vertical excitation for the anionic form, while TDDFT predicts an excitation for the neutral chromophore significantly lower than the highly correlated methods. Our findings support the picture emerging from the extrapolation of the Kamlet-Taft fit of absorption experimental data in solution and indicate that the protein gives rise to a considerable bathochromic shift with respect to vacuum. These results also open some questions on the interpretation of photodestruction spectroscopy experiments in the gas phase as well as on the accuracy of previous theoretical calculations in the more complex protein environment
143 citations
TL;DR: In this article, the heats of benzene and seven other small hydrocarbons (allyl, allene, cyclopropene, propene and propyne) have been calculated at high levels of ab initio molecular orbital theory.
Abstract: The heats of formation of benzene and seven other small hydrocarbons (allyl, allene, cyclopropene, propene, propyne, cyclopropane, and propane) have been calculated at high levels of ab initio molecular orbital theory. Geometries and frequencies were determined, in general, with coupled cluster theory, including a perturbative treatment of the connected triple excitations and with basis sets up through augmented quadruple-ζ in quality or, in some cases, augmented quintuple-ζ. Subsequent extrapolation of the total energies to the complete 1-particle basis set limit was performed, in an effort 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, atomic spin−orbit, and higher-order correlation effects. Zero-point energies were based on an average of the vibrational energies obtained from the experimental fundamentals and theoretical harmonic frequencies. Using restricted ope...
143 citations