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State Selective Equation of Motion Coupled Cluster Theory: Some Preliminary Results

Marcel Nooijen
- 30 Jun 2002 - 
- Vol. 3, Iss: 6, pp 656-675
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TLDR
A multireference variant of coupled cluster theory is described that applies to systems that can qualitatively be described by deleting two electrons from a closed shell determinant, for example biradicals, single bond breaking processes, or valence excited states.
Abstract
A multireference variant of coupled cluster theory is described that applies to systems that can qualitatively be described by deleting two electrons from a closed shell determinant, for example biradicals, single bond breaking processes, or valence excited states. The theory can be generalized to arbitrary open-shell systems and takes a form that is akin to equation-of-motion coupled cluster theory, but where all wave function parameters are explicitly optimized for the state of interest. The implementation of the present methods was accomplished in an automated fashion using the recently developed Automatic Program Generator (APG). We present benchmark results for the O 2 and F 2 molecules and investigate the behaviour of a number of closely related variants within the same general framework. Keywords: Multireference electronic structure; Coupled cluster; Electronically excited states; Automatic code generation. I. Introduction Single reference coupled cluster theory, [1,2] especially CCSD(T) [3,4], is a highly successful approach to describe the electronic structure of systems that are qualitatively reasonably well described by a single determinant (many closed-shell molecules and high-spin open-shell systems) [5-8]. Likewise coupled cluster response theory (CCLRT [9-11]) and its cousin equation-of-motion coupled cluster theory (EOM-CC [5,12]) are well suited to describe singly excited states and radicals. An important prerequisite for the applicability of the CC response approach is the presence of a nearby state that can serve as the reference in the parent state CCSD calculation. Most commonly the reference state is a closed-shell system that differs by up to one electron from the states of interest. The

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Citations
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Journal ArticleDOI

Equation-of-Motion Coupled-Cluster Methods for Open-Shell and Electronically Excited Species: The Hitchhiker's Guide to Fock Space

TL;DR: This review provides a guide to established EOM methods illustrated by examples that demonstrate the types of target states currently accessible by EOM, and touches on some formal aspects of the theory and important current developments.
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NWChem: Past, present, and future

Edoardo Aprà, +113 more
TL;DR: The NWChem computational chemistry suite is reviewed, including its history, design principles, parallel tools, current capabilities, outreach, and outlook.
Journal ArticleDOI

NWChem: Past, Present, and Future

Edoardo Aprà, +113 more
TL;DR: The NWChem computational chemistry suite as discussed by the authors provides tools to support and guide experimental efforts and for the prediction of atomistic and electronic properties by using first-principledriven methodologies to model complex chemical and materials processes.
Journal ArticleDOI

An orbital-invariant internally contracted multireference coupled cluster approach.

TL;DR: A formal analysis shows that the ic-MRCC method is invariant with respect to rotation among active orbitals, and that the orthogonalization procedure used to produce the set of linearly independent excitation operators plays a crucial role in guaranteeing the invariance properties.
References
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Journal ArticleDOI

Gaussian basis sets for use in correlated molecular calculations. I. The atoms boron through neon and hydrogen

TL;DR: In this paper, a detailed study of correlation effects in the oxygen atom was conducted, and it was shown that primitive basis sets of primitive Gaussian functions effectively and efficiently describe correlation effects.
Journal ArticleDOI

A fifth-order perturbation comparison of electron correlation theories

TL;DR: In this paper, a new augmented version of coupled-cluster theory, denoted as CCSD(T), is proposed to remedy some of the deficiencies of previous augmented coupledcluster models.
Journal ArticleDOI

On the Correlation Problem in Atomic and Molecular Systems. Calculation of Wavefunction Components in Ursell-Type Expansion Using Quantum-Field Theoretical Methods

TL;DR: In this article, a method for the calculation of the matrix elements of the logarithm of an operator which gives the exact wavefunction when operating on the wavefunction in the one-electron approximation is proposed.
Journal ArticleDOI

Convergence acceleration of iterative sequences. the case of scf iteration

TL;DR: In this article, a procedure is given for accelerating the convergence of slowly converging quasi-Newton-Raphson type algorithms for large systems of linear equations, where the number of parameters is so large that the calculation and storage of the hessian is no longer practical.
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