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Journal ArticleDOI

Applications of open-shell coupled cluster theory using an eigenvalue-independent partitioning technique: Approximate inclusion of triples in IP calculations

TL;DR: In this article, the eigenvalue-independent partitioning (EIP) approach for the calculation of open-shell coupled cluster (CC) energy differences was used to compute the ionization potentials of HF and H 2 O using basis sets with and without polarization functions.
About: This article is published in Chemical Physics Letters.The article was published on 1989-10-20. It has received 74 citations till now. The article focuses on the topics: Coupled cluster & Ground state.
Citations
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Journal ArticleDOI
TL;DR: In this article, the essential aspects of coupled-cluster theory are explained and illustrated with informative numerical results, showing that the theory offers the most accurate results among the practical ab initio electronic-structure theories applicable to moderate-sized molecules.
Abstract: Today, coupled-cluster theory offers the most accurate results among the practical ab initio electronic-structure theories applicable to moderate-sized molecules. Though it was originally proposed for problems in physics, it has seen its greatest development in chemistry, enabling an extensive range of applications to molecular structure, excited states, properties, and all kinds of spectroscopy. In this review, the essential aspects of the theory are explained and illustrated with informative numerical results.

2,667 citations

Journal ArticleDOI
TL;DR: The theory for analytic energy derivatives of excited electronic states described by the equation-of-motion coupled cluster (EOM•CC) method has been generalized to treat cases in which reference and final states differ in the number of electrons as discussed by the authors.
Abstract: The theory for analytic energy derivatives of excited electronic states described by the equation‐of‐motion coupled cluster (EOM‐CC) method has been generalized to treat cases in which reference and final states differ in the number of electrons. While this work specializes to the sector of Fock space that corresponds to ionization of the reference, the approach can be trivially modified for electron attached final states. Unlike traditional coupled cluster methods that are based on single determinant reference functions, several electronic configurations are treated in a balanced way by EOM‐CC. Therefore, this quantum chemical approach is appropriate for problems that involve important nondynamic electron correlation effects. Furthermore, a fully spin adapted treatment of doublet electronic states is guaranteed when a spin restricted closed shell reference state is used—a desirable feature that is not easily achieved in standard coupled cluster approaches. The efficient implementation of analytic gradien...

532 citations

Journal ArticleDOI
TL;DR: In this article, a new approach to the bond-breaking problem is proposed, where both closed and open shell singlet states are described within a single reference formalism as spin-flipping.

424 citations

Journal ArticleDOI
TL;DR: In this article, the major findings which have been consolidated from a broad variety of existing experiments and, at the same time, the main computational approaches which describe the extent of molecular damage following the initial electron attachment process are presented.

263 citations

Journal ArticleDOI
TL;DR: The results show that the natural occupation threshold, i.e., percentage of the total natural occupation recovered in the truncated virtual orbital space, provides a more robust truncation criterion as compared to the fixed percentage of virtual orbitals retained.
Abstract: The frozen natural orbital (FNO) approach, which has been successfully used in ground-state coupled-cluster calculations, is extended to open-shell ionized electronic states within equation-of-motion coupled-cluster (EOM-IP-CC) formalism. FNOs enable truncation of the virtual orbital space significantly reducing the computational cost with a negligible decline in accuracy. Implementation of the MP2-based FNO truncation scheme within EOM-IP-CC is presented and benchmarked using ionized states of beryllium, dihydrogen dimer, water, water dimer, nitrogen, and uracil dimer. The results show that the natural occupation threshold, i.e., percentage of the total natural occupation recovered in the truncated virtual orbital space, provides a more robust truncation criterion as compared to the fixed percentage of virtual orbitals retained. Employing 99%-99.5% natural occupation threshold, which results in the virtual space reduction by 70%-30%, yields errors below 1 kcal/mol. Moreover, the total energies exhibit linear dependence as a function of the percentage of the natural occupation retained allowing for extrapolation to the full virtual space values. The capabilities of the new method are demonstrated by the calculation of the 12 lowest vertical ionization energies (IEs) and the lowest adiabatic IE of guanine. In addition to IE calculations, we present the scans of potential energy surfaces (PESs) for ionized (H(2)O)(2) and (H(2))(2). The scans demonstrate that the FNO truncation does not introduce significant nonparallelity errors and accurately describes the PESs shapes and the corresponding energy differences, e.g., dissociation energies.

115 citations

References
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TL;DR: In this paper, the effects of contraction on the energies and one-electron properties of the water and nitrogen molecules were investigated, and the authors obtained principles which can be used to predict optimal contraction schemes for other systems without the necessity of such exhaustive calculations.
Abstract: The contraction of Gaussian basis functions for use in molecular calculations is investigated by considering the effects of contraction on the energies and one‐electron properties of the water and nitrogen molecules. The emphasis is on obtaining principles which can be used to predict optimal contraction schemes for other systems without the necessity of such exhaustive calculations. Using these principles, contractions are predicted for the first‐row atoms.

4,595 citations

Journal ArticleDOI
TL;DR: In this article, the use of a linear combination of Gaussian type orbitals (CGTO) instead of an individual Gaussian-type orbital (GTO) as a unit of basis functions for large-scale molecular calculations is discussed.
Abstract: The use of a linear combination of Gaussian‐type orbitals (CGTO), instead of an individual Gaussian‐type orbital (GTO), as a unit of basis functions for large‐scale molecular calculations, is discussed. A systematic construction of the CGTO basis functions is attempted and the results for the atoms from Li through Ar are reported.

3,257 citations

Journal ArticleDOI
TL;DR: Manybody perturbation theory (MBPT) and coupled-cluster methcoder (CCM) were defined in this paper as a subset of the N-body problem.
Abstract: Ten years ago in the Annual Review of Physical Chemistry. there was a review article entitled "Many-Body Theories of the Electronic Structure of Atoms and Molecules," by Karl Freed ( 1 ) . In that article many-body methods were defined to be those techniques which derive their impetus from theories of the N-body problem for which N --+ 00. For the purposes of this review, we further specify these methods as many-body perturba­ tion theory (MBPT) (2-5) and the closely related coupled-cluster meth­ ods (CCM) (6-9) . In the ten years since that review appeared, probably no area in theo­ retical chemistry has undergone more development than has the theory, methodology, and applications of such ab initio many-body methods for

1,861 citations

Journal ArticleDOI
TL;DR: In this article, the authors study the open-shell coupled-cluster theories and examine the current theoretical status regarding the existence or non-existence of a linked-clusters theorem, ensuring the connectedness of the cluster amplitudes and the effective Hamiltonian.

416 citations