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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 relativistic correction is obtained by applying direct perturbation theory through the first order, and it is shown that its implementation is straightforward if analytical energy gradients of the methods under consideration are available.
Abstract: The computation of the relativistic correction to the first order in 1/c2, where c is the velocity of light, is implemented at the levels of coupled cluster and many-body perturbation theory. The relativistic correction is obtained by applying direct perturbation theory through the first order, and it is shown that its implementation is straightforward if analytical energy gradients of the methods under consideration are available. Preliminary results were obtained by a numerical procedure and are reported for some closed-shell atoms (He, Be, Ne, and Ar) and molecules (CuH and SiH4). © 1997 by John Wiley & Sons, Inc.
82 citations
TL;DR: In this article, a coupled cluster and manybody perturbation theory methods that include triple excitation effects were applied to the determination of the quartic force field of the water molecule using an extended Slater-type basis set.
Abstract: Ab initio coupled cluster and many‐body perturbation theory methods that include triple excitation effects are applied to the determination of the quartic force field of the water molecule using an extended Slater‐type basis set. Predictions of fundamental, overtone, and combination vibrational frequencies, rotational constants, and vibration–rotation coupling constants are reported for H2O and its isotopomers. The best predicted harmonic frequencies for the stretching modes of H2O are accurate to 3 cm−1, while the bending mode has an error of 28 cm−1. The mean absolute error for all frequencies reached by two quanta is 0.6%, while the anharmonic constants xi j have a mean absolute error of less than 3%. The important role of triple excitation effects in the surface determination is discussed, and is compared with the effects of quadruple excitations.
81 citations
TL;DR: Response theory in the context of vibrational coupled cluster (VCC) theory is introduced and used to obtain vibrational excitation energies and the increase in accuracy of VCC response energies relative to VCI energies is discussed theoretically in terms of a perturbational order expansion and demonstrated numerically.
Abstract: Response theory in the context of vibrational coupled cluster (VCC) theory is introduced and used to obtain vibrational excitation energies. The relation to the vibrational configuration interaction (VCI) approach is described, and the increase in accuracy of VCC response energies relative to VCI energies is discussed theoretically in terms of a perturbational order expansion and demonstrated numerically. To illustrate the theory, a pilot implementation is used to obtain anharmonic vibrational frequencies for fundamental, first overtone and combination excitations of formaldehyde as well as for the fundamental transitions of ethylene.
81 citations
TL;DR: Hydricity can be used as a practical guide in future catalyst design and is found to be the hydride transfer in CO2 hydrogenation catalyzed by the Fe(II) complex that possesses moderate hydricity traverses an H2-splitting RDS, whereas the RDS for the high-hydricity Co(III) species is foundto be the Hydride Transfer.
Abstract: The development of efficient catalysts with base metals for CO2 hydrogenation has always been a major thrust of interest. A series of experimental and theoretical work has revealed that the catalytic cycle typically involves two key steps, namely, base-promoted heterolytic H2 splitting and hydride transfer to CO2, either of which can be the rate-determining step (RDS) of the entire reaction. To explore the determining factor for the nature of RDS, we present herein a comparative mechanistic investigation on CO2 hydrogenation mediated by [M(H)(η2-H2)(PP3Ph)]n+ (M = Fe(II), Ru(II), and Co(III); PP3Ph = tris(2-(diphenylphosphino)phenyl)phosphine) type complexes. In order to construct reliable free energy profiles, we used highly correlated wave function based ab initio methods of the coupled cluster type alongside the standard density functional theory. Our calculations demonstrate that the hydricity of the metal–hydride intermediate generated by H2 splitting dictates the nature of the RDS for the Fe(II) and...
81 citations
TL;DR: In this article, the performances of different density functionals and basis sets in the computation of anharmonic frequencies of semirigid molecules by a second-order perturbative treatment have been evaluated with reference to coupled cluster computations.
81 citations