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Showing 1 to 14 of 14 for “"coupled cluster theory"”.
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Stochastic Approaches to Coupled Cluster Theory
… of various new approaches to solving the Coupled Cluster (CC) equations through Monte Carlo (MC) integration. Firstly, exact importance sampling of the CC wavefunction to arbitrary order is defined and applied as a modification to the extant unlinked Coupled Cluster Monte Carlo (CCMC) …
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Development of multicomponent coupled-cluster theory and its application to nanoclusters and molecular systems
… the motion of the two particle types is decoupled. While the BO approximation is ubiquitous in computational and theoretical studies, it is not always justifiable. There are two main cases where this approximation is not valid. The first is when nuclear and electronic motion cannot be …
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Towards an Improved Method for the Prediction of Linear Response Properties of Small Organic Molecules
… averaging and time-dependent density functional theory calculations that incorporate solvent molecules explicitly in the quantum mechanical region. While considering several controllable parameters along which the system's optical rotation varies, we find that the sampling of the dynamical …
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Novel Quantum Chemistry Algorithms Based on the Variational Quantum Eigensolver
… equations similar to those of the linearized coupled cluster theory (LCCSD) but is more systematically improvable and, for X = 3 or X = ∞, can break single bonds, which LCCSD cannot do. The overall aim of this work is to showcase the richness of the VQE algorithm and the breadth of its …
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Quartic Force Fields for Electronically Excited States of Interstellar Molecules
… presented herein using equation-of-motion (EOM) coupled cluster theory. The new EOM-based QFF is tested against the traditional QFF method using the isoformyl (HOC) radical’s variationally accessible 1 A” excited state and compared to previous benchmark studies. Challenges presented in this study …
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Lie algebraic similarity transformations: improving wavefunctions for weak and strong correlations
… unbound, projective equations in the spirit of coupled cluster theory lead to well-defined solutions. The theory is tested on the one and two-dimensional repulsive Hubbard model where it yields accurate results for large systems with low computational cost. Symmetry projection methods are …
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Ab initio Calculations of Optical Rotation
Coupled cluster (CC) and density functional theory (DFT) are highly regarded as robust quantum chemical methods for accurately predicting a wide variety of properties, such as molecular structures, thermochemical data, vibrational spectra, etc., but there has been little focus on the theoretical …
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Local Correlation: Implementation and Application to Molecular Response Properties
… and later to Møller-Plesset perturbation theory. Werner et al. have have extended the local correlation scheme of Pulay and Saebø to coupled-cluster theory. One of the pitfalls of the local correlation methods developed by Pulay and Saebø is the dependence of domain selection on the …
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It's Not a SKZCAM! Accurate Surface Chemistry at Low Cost
… going beyond the standard density functional theory (DFT) to methods like coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. However, the high computational cost of CCSD(T) typically necessitates the use of embedded cluster models, where the surface is …
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Theoretical Prediction of Electronically Excited States and Vibrational Frequencies of Interstellar and Planetary Radicals, Anions, and Cations
… as well as the cis-HOCO anion. First, open-shell coupled cluster methods of singles and doubles (CCSD) and singles and doubles with triples-inclusion (CC3) are tested on the C₂H and C₄H radicals. The significant double-excitation character, as well as the quartet multiplicity of some states yields …
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Towards a Reduced-Scaling Method for Calculating Coupled Cluster Response Properties
… with the size of the system. For example, the coupled cluster singles and doubles method with the perturbative inclusion of triples: the CCSD(T) model, which is considered to be the ``gold standard'' of quantum chemistry scales as 𝑂(N⁷) in its canonical formulation, where $N$ is a measure of …
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Development and Application of Coupled Cluster Ground- and Excited-State Models
… monocyclic form. At the CCSDT/6-31G** level of theory, the C1–C3 distance of the minimum energy form of m-benzyne is 2.0°A and the profile of the PES along the C1–C3 distance is that of an asymmetric, single-well, in agreement with previous density-functional theory and coupled cluster studies. …
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Breaking the curse of dimensionality in electronic structure methods: towards optimal utilization of the canonical polyadic decomposition
… to develop reduced-scaling electronic structure theory methods using the CP decomposition. In Chapter 2, we introduce the robust tensor network approximation. This approximation is a way to, in general, eliminate the leading-order error associated with approximated tensors in a network. We …
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Comparison of Calculated Normal Mode Molecular Vibrations with Experimental Gas-Phase Infrared Spectroscopy
… compared to experimental values. Couple cluster theory (CC) yields quite accurate calculations for diatomic molecules. Whereas, with polyatomic H<sub>2</sub>O, CH<sub>4</sub> and CH<sub>2</sub>O required a time of 45 minutes to 1 hour with variation of ± 0 to 20 cm<sup>-1</sup>. For …