Pair-correlated coupled cluster theory: An alternative multireference coupled cluster method

2003 ◽  
Vol 118 (13) ◽  
pp. 5736-5745 ◽  
Author(s):  
Shuhua Li ◽  
Jing Ma ◽  
Yuansheng Jiang
Keyword(s):  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Coupled Cluster Theory ◽  
Cluster Theory

Multireference State-Specific Coupled-Cluster Theory and Multiconfigurationality Index. BH Dissociation

2005 ◽  
Vol 70 (7) ◽  
pp. 1017-1033 ◽  
Author(s):  
Vladimir V. Ivanov ◽  
Ludwik Adamowicz ◽  
Dmitry I. Lyakh
Keyword(s):  
Wave Function ◽  
Numerical Results ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Coupled Cluster Theory ◽  
Cluster Theory ◽  
Computer Aided

Multiconfigurationality index calculated for the coupled-cluster wave function based on an algorithm developed using a computer-aided generation approach is applied to analyze the multireference state-specific coupled-cluster method with the CAS reference (i.e. the so called the CAS(n,m)CCSD approach). The numerical results concern dissociation of the BH molecule where at larger displacement from the equilibrium significant quasi-degeneracy arises. The analysis shows that the CAS(n,m)CCSD approach performs very well in such a situation.

Time-Independent Coupled-Cluster Theory of the Polarization Propagator

2005 ◽  
Vol 70 (8) ◽  
pp. 1109-1132 ◽  
Author(s):  
Robert Moszynski ◽  
Piotr S. Żuchowski ◽  
Bogumił Jeziorski
Keyword(s):  
Order Term ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Cluster Approach ◽  
Coupled Cluster Theory ◽  
Cluster Theory ◽  
Polarization Propagator ◽  
Apparent Correlation ◽  
Moller Plesset ◽  
New Formulation

A novel, time-independent formulation of the coupled-cluster theory of the polarization propagator is presented. This formulation, unlike the equation-of-motion coupled-cluster approach, is fully size-extensive and, unlike the conventional time-dependent coupled-cluster method, is manifestly Hermitian, which guarantees that the polarization propagator is always real for purely imaginary frequencies and that the resulting polarizabilities exhibit time-reversal symmetry (are even functions of frequency) for purely real or purely imaginary perturbations. This new formulation is used to derive compact expressions for the three leading terms in the Møller-Plesset expansion for the polarization propagator. The true and apparent correlation contributions to the second-order term are analyzed and separated at the operator level. Explicit equations for the polarization propagator at the non-perturbative, singles and doubles level (CCSD) are presented.

Electronic Spectra and Ionization Potentials of Halogen Oxides Using the Fock Space Coupled-Cluster Method

2005 ◽  
Vol 70 (7) ◽  
pp. 851-863 ◽  
Author(s):  
Nayana Vaval ◽  
Prashant Manohar ◽  
Sourav Pal
Keyword(s):  
Excited States ◽  
Fock Space ◽  
Ionization Potentials ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Excitation Energies ◽  
Coupled Cluster Theory ◽  
Vertical Detachment Energy ◽  
Halogen Oxides

The ionization potentials and excitation energies of halogen monoxides and dihalogen oxides are studied using fully size-extensive Fock space version of multi-reference coupled-cluster theory. The low-lying excited states of ClO-, FO-, Cl2O and F2O are obtained along with the ionization spectra of Cl2O and F2O. The adiabatic electron affinity of ClO, FO and the vertical detachment energy of ClO- and FO- are also presented.

The relativistic coupled-cluster method: transition energies of bismuth and eka-bismuth

1998 ◽  
Vol 94 (1) ◽  
pp. 181-187 ◽  
Author(s):  
EPHRAIM ELIAV ◽  
UZI KALDOR ◽  
YASUYUKI ISHIKAWA
Keyword(s):  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Transition Energies

A Multi-Layer Approach to the Equation of Motion Coupled-Cluster Method for the Electron Affinity

2020 ◽  
Author(s):  
Soumi Haldar ◽  
Achintya Kumar Dutta
Keyword(s):  
Electron Affinity ◽  
Electron Attachment ◽  
Equation Of Motion ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Coupled Cluster Method ◽  
Large Molecules ◽  
Layer Method ◽  
Speed Up ◽  
Attachment Process

We have presented a multi-layer implementation of the equation of motion coupled-cluster method for the electron affinity, based on local and pair natural orbitals. The method gives consistent accuracy for both localized and delocalized anionic states. It results in many fold speedup in computational timing as compared to the canonical and DLPNO based implementation of the EA-EOM-CCSD method. We have also developed an explicit fragment-based approach which can lead to even higher speed-up with little loss in accuracy. The multi-layer method can be used to treat the environmental effect of both bonded and non-bonded nature on the electron attachment process in large molecules.<br>

Excitonic Coupled-cluster Theory: Part I, General Formalism

2017 ◽  
Author(s):  
Yuhong Liu ◽  
Anthony Dutoi
Keyword(s):  
Electron Correlation ◽  
Degrees Of Freedom ◽  
Model Systems ◽  
Coupled Cluster ◽  
Effective Hamiltonian ◽  
Coupled Cluster Theory ◽  
Cluster Theory ◽  
Companion Article ◽  
High Level ◽  
Fragment Interaction

<div> <div>A shortcoming of presently available fragment-based methods is that electron correlation (if included) is described at the level of individual electrons, resulting in many redundant evaluations of the electronic relaxations associated with any given fluctuation. A generalized variant of coupled-cluster (CC) theory is described, wherein the degrees of freedom are fluctuations of fragments between internally correlated states. The effects of intra-fragment correlation on the inter-fragment interaction is pre-computed and permanently folded into the effective Hamiltonian. This article provides a high-level description of the CC variant, establishing some useful notation, and it demonstrates the advantage of the proposed paradigm numerically on model systems. A companion article shows that the electronic Hamiltonian of real systems may always be cast in the form demanded. This framework opens a promising path to build finely tunable systematically improvable methods to capture precise properties of systems interacting with a large number of other systems. </div> </div>

Excitonic Coupled-cluster Theory: Part I, General Formalism

2017 ◽  
Author(s):  
Yuhong Liu ◽  
Anthony Dutoi
Keyword(s):  
Electron Correlation ◽  
Degrees Of Freedom ◽  
Model Systems ◽  
Coupled Cluster ◽  
Effective Hamiltonian ◽  
Coupled Cluster Theory ◽  
Cluster Theory ◽  
Companion Article ◽  
High Level ◽  
Fragment Interaction

<div> <div>A shortcoming of presently available fragment-based methods is that electron correlation (if included) is described at the level of individual electrons, resulting in many redundant evaluations of the electronic relaxations associated with any given fluctuation. A generalized variant of coupled-cluster (CC) theory is described, wherein the degrees of freedom are fluctuations of fragments between internally correlated states. The effects of intra-fragment correlation on the inter-fragment interaction is pre-computed and permanently folded into the effective Hamiltonian. This article provides a high-level description of the CC variant, establishing some useful notation, and it demonstrates the advantage of the proposed paradigm numerically on model systems. A companion article shows that the electronic Hamiltonian of real systems may always be cast in the form demanded. This framework opens a promising path to build finely tunable systematically improvable methods to capture precise properties of systems interacting with a large number of other systems. </div> </div>

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