scispace - formally typeset
Search or ask a question
Topic

Coupled cluster

About: Coupled cluster is a research topic. Over the lifetime, 6280 publications have been published within this topic receiving 301055 citations.


Papers
More filters
Journal ArticleDOI
TL;DR: The theoretical dissociation energy for the H3O+−H2O system is predicted to be 33.4 kcal/mol, and is in good agreement with experimental measurements as mentioned in this paper.
Abstract: Ab initio quantum mechanical methods have been applied to the H5O+2 system, for which experiments are beginning to appear. These methods include basis sets up to triple‐ζ plus double polarization plus f functions (TZ2Pf ) and levels of correlation up to coupled cluster including single, double, and perturbatively treated connected triple excitations [CCSD(T)]. The potential energy hypersurface is very flat and is sensitive to the level of theory. At the highest level of theory the global minimum is the structure with C2 symmetry, but the transition state with Cs symmetry is only 0.4 kcal/mol higher in energy. Some low energy excursions into C1 symmetry are carefully examined. The theoretical dissociation energy for the H3O+–H2O system is predicted to be 33.4 kcal/mol, and is in good agreement with experimental measurements. The harmonic vibrational frequencies and their infrared intensities at several levels of theory are also reported, and compared to the recent spectroscopic observations in Lee’s labora...

167 citations

Journal ArticleDOI
TL;DR: In this paper, a generalized version of the multireference coupled-cluster method using a single reference formalism has been implemented, where the single and double excitations from the secondary reference determinants have been truncated to include only those that correspond to triple excitations of the formal reference determinant.
Abstract: A generalized version of the multireference coupled‐cluster method using a single‐reference formalism, which we presented in an earlier paper, has been implemented. Any number of determinants, that differ from the formal reference determinant by single or double excitations, can now be included in the reference space. In the present implementation, the single and double excitations from the secondary reference determinants have been truncated to include only those that correspond to triple excitations from the formal reference determinant. Calculations are done on a few model systems, LiH, BH, and H2O, at equilibrium and stretched geometries. Comparisons are made with full configuration interaction (CI) treatment for the single bond stretch in LiH and BH, and the results are quite promising. For the water molecule, comparisons are made with the results obtained with the coupled cluster method truncated at triple excitations (CCSDT), as well as with the full CI results. While the multireference method did not do as well for the simultaneous two‐bond stretch in H2O as it did for the single bond cases, it did at least as well as the CCSDT at representing the points on the full CI potential curve.

167 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the unusual potential energy curve for the 1∑+g ground state of Be2 using manybody perturbation theory (MBPT) and coupled-cluster (CC) methods.
Abstract: The unusual potential energy curve for the 1∑+g ground state of Be2 is investigated using many‐body perturbation theory (MBPT) and coupled‐cluster (CC) methods. The curve, which has a ∼2 kcal/mol inner minimum at ∼2.6A and a van der Waals minimum at ∼5.0 A, is very difficult to describe accurately with even high‐level ab initio correlated methods. To resolve uncertainties in previous MBPT/CC studies, we have generalized CC theory to include effects of triple excitations. The present calculations are compared with recent full CI results to assess the relative importance of different contributions of electron correlation. MBPT (4) is found to be qualitatively correct, but to slightly exceed the correct full CI binding energy, while CC theory even with triple excitations, has no inner minimum. The latter follows from CC theory being exact for separated Be atoms (with frozen core) but to have a 1% correlation energy error in the binding region. Yet this 1% accounts for the ∼2 kcal/mol inner well. The possibil...

166 citations

Journal ArticleDOI
TL;DR: In this paper, a new way to compute the external exchange matrices in the local coupled cluster (LCC) theory is presented, which eliminates the most important bottleneck of linear scaling LCC methods.
Abstract: A new way to compute the external exchange matrices in the local coupled cluster (LCC) theory is presented, which eliminates the most important bottleneck of our previous linear scaling LCC methods. It is based on a decomposition of the transformed two-electron integral set involving four external indices into blocks belonging to quadruples of atoms. A new additional transformation module was developed, which generates this very compact 4-external integral set before the LCC iteration loop is entered. The length of this integral set and the computational cost for producing it scale linearly with molecular size. Using these precomputed integrals, their contraction with the amplitudes, i.e. the assembly of the external exchange matrices occurring in each LCC iteration now is performed directly in the (external) space of the projected AOs (AOs, atomic orbitals) rather than in AO basis as previously, and proceeds exceedingly fast (3 min compared to 15 h with our previous algorithm, for the largest test-molecule considered in this paper).

166 citations

Journal ArticleDOI
TL;DR: This work features an analysis for the acceleration technique DIIS that is standardly used in most of the important quantum chemistry codes, e.g. in DFT and Hartree–Fock calculations and in the Coupled Cluster method and shows that for the general nonlinear case, DIIS corresponds to a projected quasi-Newton/secant method.
Abstract: This work features an analysis for the acceleration technique DIIS that is standardly used in most of the important quantum chemistry codes, e.g. in DFT and Hartree–Fock calculations and in the Coupled Cluster method. Taking up results from Harrison (J Comput Chem 25:328, 2003), we show that for the general nonlinear case, DIIS corresponds to a projected quasi-Newton/secant method. For linear systems, we establish connections to the well-known GMRES solver and transfer according (positive as well as negative) convergence results to DIIS. In particular, we discuss the circumstances under which DIIS exhibits superlinear convergence behaviour. For the general nonlinear case, we then use these results to show that a DIIS step can be interpreted as step of a quasi-Newton method in which the Jacobian used in the Newton step is approximated by finite differences and in which the according linear system is solved by a GMRES procedure, and give according convergence estimates.

166 citations


Network Information
Related Topics (5)
Ab initio
57.3K papers, 1.6M citations
94% related
Excited state
102.2K papers, 2.2M citations
88% related
Ground state
70K papers, 1.5M citations
88% related
Molecule
52.4K papers, 1.2M citations
85% related
Electronic structure
43.9K papers, 1.1M citations
84% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023163
2022351
2021267
2020344
2019253
2018244