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# Topic: Coupled cluster

###### In the News (Tue 20 Aug 19)

 Coupled cluster - Wikipedia, the free encyclopedia Coupled cluster (CC) method is a technique used for description of the many-body systems. Hilbert space coupled cluster), valence-universal coupled cluster (a.k.a. The coupled cluster equations are usually derived using diagrammatic technique and result in nonlinear equations which can be solved in an iterative way. en.wikipedia.org /wiki/Coupled_cluster   (545 words)

 Computer cluster - Wikipedia, the free encyclopedia Clusters are usually deployed to improve speed and/or reliability over that provided by a single computer, while typically being much more cost-effective than single computers of comparable speed or reliability. High-availability clusters are implemented primarily for the purpose of improving the availability of services which the cluster provides. High-performance clusters are implemented primarily to provide increased performance by splitting a computational task across many different nodes in the cluster, and are most commonly used in scientific computing. en.wikipedia.org /wiki/Computer_cluster   (1039 words)

 An Eigenvalue Approach to Coupled Cluster Theory   (Site not responding. Last check: 2007-10-08) The coupled cluster Schrödinger equation'', which leads to the energy and amplitude expressions given in Eqs. The concept of the coupled cluster method as an eigenvalue problem may be easily generalized to include excited states (in this case, states that are not the lowest in energy within a given symmetry). (where the cluster amplitudes are taken from the corresponding CCSD ground-state energy calculation) in the space of all singly and doubly excited determinants. zopyros.ccqc.uga.edu /lec_top/cc/html/node10.html   (774 words)

 Coupled cluster -- Facts, Info, and Encyclopedia article   (Site not responding. Last check: 2007-10-08) Coupled cluster method is a technique used for description of the (additional info and facts about many-body system) many-body systems. In the above formulae and denote the creation and annihilation (An agent that operates some apparatus or machine) operators and i,j stand for occupied and a,b for unoccupied orbitals. The method gives exact non- (additional info and facts about relativistic) relativistic solution of the (additional info and facts about Schrödinger equation) Schrödinger equation of the n-body problem if one includes up to the cluster operator. www.absoluteastronomy.com /encyclopedia/c/co/coupled_cluster.htm   (227 words)

 Introduction   (Site not responding. Last check: 2007-10-08) The purpose of this chapter is to provide computational chemists who seek a deeper knowledge of coupled cluster theory with the background necessary to understand the extensive literature on this important ab initio technique. In spite of the method's present utility and popularity, the quantum chemical community was slow to accept coupled cluster theory, perhaps because the earliest researchers in the field used elegant but unfamiliar mathematical tools such as Feynman-like diagrams and second-quantization to derive working equations. 78], this chapter is unique in that it attempts to provide a concise, practical introduction to the mathematical techniques of coupled cluster theory (both algebraic and diagrammatic), as well as a discussion of the efficient implementation of the method on high-performance computers, in a manner accessible to newcomers to the field. zopyros.ccqc.uga.edu /lec_top/cc/html/node1.html   (630 words)

 High-performance Linux clustering, Part 1: Clustering fundamentals Clusters are the predominant type of HPC hardware these days; a cluster is a set of MPPs. Clusters are built using commodity hardware and cost a fraction of the vector processors. Clusters use a message-passing paradigm for communication, and programs have to be explicitly coded to make use of distributed hardware. www.ibm.com /developerworks/linux/library/l-cluster1   (2849 words)

 Encyclopedia: Coupled cluster   (Site not responding. Last check: 2007-10-08) is the cluster operator: In computational physics and computational chemistry, the Hartree-Fock (HF) or self-consistent field (SCF) calculation scheme is a self-consistent iterative variational procedure to calculate the Slater determinant (or the molecular orbitals which it is made of) for which the expectation value of the electronic molecular Hamiltonian is minimum. This article is about operators in mathematics, for other kinds of operators see operator (disambiguation). Albert Einsteins theory of relativity is a set of two theories in physics: special relativity and general relativity. www.nationmaster.com /encyclopedia/Coupled-cluster   (729 words)

 Scientific Discovery through Advanced Computing (SciDAC) -- Biology and Environment Project This project will expand the applicability of coupled cluster electronic structure methods to include molecular bond breaking and transition state structures. A new method of moments of coupled cluster equations and renormalization approach will be developed for ground electronic states, and an active space equation-of-motion coupled cluster method will be developed for electronically excited states. In addition, the method of moments of coupled cluster equations will be extended to electronically excited states via the equation-of-motion coupled cluster formalism. www.osti.gov /scidac/bes/projects/piecuch.html   (115 words)

 [No title] Large dependence on the size of the cluster, level of methodological refinement, and accuracy of implementation (basis set) are found. The same ordering is found for the BeLik clusters which indicates a departure from the ordering found in pure alkali clusters by the lowering of the 2s level to below the ld level due to the larger electron affinity of the (usually) centered Be impurity. This analysis also allows us to observe an increasingly metallic behavior with cluster size, by associating the electron density distribution, and in the case of a charged cluster, the distribution of the hole, with atomic sites, and with regions of overlap between atom pairs. www.qtp.ufl.edu /kdi/ContPres/Abstracts.html   (2729 words)

 Cluster Infrastructure for Linux (CI) This project is developing a common infrastructure for Linux clustering by extending the CLuster Membership Subsystem ("CLMS") and Internode Communication Subsystem ("ICS") of the OpenSSI project. Provide a cluster infrastructure that can be used as the basis for many different cluster products and projects, including HA failover, load leveling, parallel filesystem, HPC and Single System Image (SSI). Support for hierarchical clusters has been requested, where the impact might be that non-core nodes wouldn't be monitored for nodedown nearly as frequently as core nodes containing resources that have to be quickly recovered. ci-linux.sourceforge.net   (1117 words)

 Invited Lectures   (Site not responding. Last check: 2007-10-08) Coupled Cluster Theory and its Applications to Molecular Electronic Structure, Department of Chemistry, Rice University, Houston, Texas, December 5, 1988. Coupled Cluster Theory and its Applications to Molecular Electronic Structure, Department of Chemistry, University of California, Berkeley, California, January 26, 1989. Application of Open-Shell Coupled Cluster Theory to As2, Ga2 and GaAs Workshop on Coupled Cluster Theory at the Interface of Atomic Physics and Quantum Chemistry, Institute for Theoretical Atomic and Molecular Physics at the Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, August 8, 1990. pchem1.rice.edu /~guscus/lectures.html   (2923 words)

 [No title]   (Site not responding. Last check: 2007-10-08) In between loosely-coupled clusters and tightly coupled CC-NUMA symmetric multiprocessors (SMP), Dolphin is exploring what we call the Shared Memory Cluster (SMC), which, at the operating system level looks like a typical cluster, but presents a single system image to applications. The SMC cluster has advantages over both the loosely-coupled cluster and the tightly-coupled SMP. But unlike most clusters, an SMC system presents programs with the shared memory model expected by a wide range of existing applications. www-csag.ucsd.edu /individual/achien/asplos/posters/sci.txt   (488 words)

 Coupled Cluster:   (Site not responding. Last check: 2007-10-08) Coupled Cluster: CCSD and CCSD(T) Coupled Cluster (CC) calculations are performed under control of RUNTYPE CI, with the nature of the CC defined by a data line with CCSD or CCSD(T) in the first datafield. Coupled Cluster treatments are limited to closed shell systems; no gradients are available at present. ACTIVE and CORE directives may be used to control the final set of MOs to feature in the calculation. www.cfs.dl.ac.uk /tutorials/gamess-uk_LCSC.2/sld039.htm   (76 words)

 Evaluation of Applications on a Loosely-Coupled Cluster (ResearchIndex)   (Site not responding. Last check: 2007-10-08) Currently, the ATM network cluster consists of Sun, Silicon Graphics, and Intel-based workstations. The purpose of the ATM cluster testbed is twofold, one is production and the other is research. The production focus is concerned with evaluating the benefit of bringing ATM to the desktop and determining the scalability and viability of such an environment for some... citeseer.ist.psu.edu /436775.html   (345 words)

 Electronic Spectroscopy and Photochemistry of Small Transition Metal Complexes The second aspect related to the calculation of accurate multidimensional PES describing the reactivity of various electronic excited states is the actual bottleneck of the theoretical study. These calculations will be based on the expertise of the group in highly correlated Coupled Cluster methods for determination of accurate molecular properties. The expertise of the Strasbourg group in the use of wavepacket propagations to describe photochemical processes in a variety of transition metal complexes will guarantee the success and the feasibility of this original and ambitious project in a reasonable time scale. www.chem.ufl.edu /~duran/IGERT/bartlett_strich.htm   (1589 words)

 GAMESS Documentation: Further Information The code is designed to converge in relatively few iterations for significantly stretched nuclear geometries, where it is not unusual to obtain large cluster amplitudes whose absolute values are close to 1. User performs an extra calculation for a different nuclear geometry, for which it is easier to converge the CCSD equations, and restarts the calculation from the restart file generated by an extra calculation. This technique of restarting the CC calculations from the cluster amplitudes obtained for a neighboring nuclear geometry is particularly useful for scanning PESs and for calculating energy derivatives by numerical differentiation. myweb.liu.edu /~nmatsuna/gamess/refs/howto.cc.html   (1964 words)

 Dr. Rodney J. Bartlett's Bio Coupled-cluster methods offer such an accurate evaluation of electron correlation that, when combined with extrapolated basis sets, definitive results can be obtained for molecular energies and other properties. In recent work he and his group have introduced Ab Initio Density Functional Theory as the connecting link between wavefunction theory and DFT17-19 and have focused their theoretical NMR effort on the important issue of coupling constants across H-bonds20-22, and their role in determining biomolecular structures. Musial, S. Kucharski, and R. Bartlett, "Coupled cluster study of the triple bond," Chem. www.chem.ufl.edu /~ccp/bartlett.htm   (678 words)

 C (1) channel coupling array (quantum theory for atoms and molecules) (2) close-coupling approximation (3) coupled-cluster approach (4) crystalline cluster approach (in electronic structure calcns.) (1) convergent close coupling (2) correlated coupled cluster (quantum calcn. coupled cluster method with single and double replacements - G. Purvis and R. Bartlett, J. www.iupac.org /reports/1996/6802brown/c.html   (1081 words)

 Formal Coupled Cluster Theory   (Site not responding. Last check: 2007-10-08) The exponential ansatz described above is essential to coupled cluster theory, but we do not yet have a recipe for determining the so-called cluster amplitudes'' (t Additionally, one may obtain expressions for the cluster amplitudes by left-projecting the Schrödinger equation by the excited determinants produced by the action of the cluster operator, Furthermore, they are formally exact; if the cluster operator, zopyros.ccqc.uga.edu /lec_top/cc/html/node6.html   (150 words)

 APS - 2005 36th Meeting of the Division of Atomic, Molecular and Optical Physics PostDeadline - Event - Calculation of ...   (Site not responding. Last check: 2007-10-08) This work is aimed at the complete restoration of the non-linear coupled-cluster terms at the SD level. Among the numerous types of non-linear coupled- cluster terms, only six will contribute to the single or double all-order equations. We have derived expressions for all six of those terms, conducted the angular reduction, and modified the single and double all-order equations accordingly. meetings.aps.org /Meeting/DAMOP05/Event/30784   (239 words)

 Research topics In recent years several new techniques for excited states (DFT/MRCI and MR-MP2) have been developed and together with the well known TDDFT method we have investigated the electronic spectra of the diverse set of the molecules. Calculations on electronic states with very different character not only help to assess the accuracy and the applicability of the different theoretical methods but allow quantitative prediction and analysis of electronic spectra. Some other approaches are also known to exist: atomic orbital coupled cluster (AO-CCSD) proposed by Scuseria and the local treatment of coupled cluster (LCCSD) implemented by Werner and Schütz. www.uni-muenster.de /Chemie.oc/research/grimme/abstract.html   (1869 words)

 ACS/COMP: Division Programming A locally correlated equation-of-motion coupled cluster approach for excited states of large molecules. Coupled cluster methods for high accuracy and bond-breaking. The combination of molecular modeling with residual dipolar coupling in NMR spectroscopy for conformations of complex oligosaccharides. membership.acs.org /c/comp/pastprograms/sp02.html   (2836 words)

 IngentaConnect On the generalized multi-reference Brillouin-Wigner coupled clust...   (Site not responding. Last check: 2007-10-08) The generalized multireference Brillouin-Wigner coupled cluster theory is presented for the case of a single root function. The Bloch-like equation and the Lippmann-Schwinger-like equation for the generalized multireference Brillouin-Wigner perturbation theory are obtained. These equations are then applied to the solution of the multireference coupled cluster equations for the case in which a single root function is required. api.ingentaconnect.com /content/iop/jphysb/2001/00000034/00000021/art00314   (166 words)

 APS - 2005 APS March Meeting PostDeadline - Event - Coupled Cluster Approximation to the \emph{t-J} Model   (Site not responding. Last check: 2007-10-08) Abstract: R1.00029 : Coupled Cluster Approximation to the \emph{t-J} Model We study the ground state of the one-dimensional \emph{t-J} model with a single hole using the well known Coupled Cluster Method (CCM). The Hamiltonian includes a kinetic energy term \emph{t} which represents electron hopping from atomic site to atomic site with a probability which is proportional to the overlap of their (localized) wave functions. meetings.aps.org /Meeting/MAR05/Event/27899   (177 words)

 IngentaConnect High-order coupled cluster method calculations for the ground- an...   (Site not responding. Last check: 2007-10-08) IngentaConnect High-order coupled cluster method calculations for the ground- an... High-order coupled cluster method calculations for the ground- and excited-state properties of the spin-half XXZ model In this article, we present new results of high-order coupled cluster method (CCM) calculations, based on a N?el model state with spins aligned in the z-direction, for both the ground- and excited-state properties of the spin-half XXZ model on the linear chain, the square lattice, and the simple cubic lattice. api.ingentaconnect.com /content/iop/jphyscm/2000/00000012/00000030/art00317   (354 words)

 Size-consistent wave functions for nondynamical correlation energy: The valence actiev space optimized orbital ...   (Site not responding. Last check: 2007-10-08) The simplest member of this hierarchy involves connected double excitations within the variationally optimized valence active space and may be denoted as VOO-CCD, or VOD. VOO-CCD is size-consistent, has computational complexcity proportional to the sixth power of molecule size, and is expected to accurately approximate the nondynamical correlation energy in such cases as single bond dissociation, diradicals, and anti-ferromagnetic coupling. We report details of our implementation of VOO-CCD and illustrate that it does indeed accurately recover the nondynamical correlation energy for challenging multireference problems such as the torsion of ethylene and chemical bond breaking. vergil.chemistry.gatech.edu /pubs/abstracts/vooccd.html   (248 words)

 Scientific Discovery through Advanced Computing (SciDAC) -- Biology and Environment Project Efficient methods will be developed for incorporating dynamical electron correlation effects into molecular quantum mechanics by using basis sets that depend explicitly on the inter-electronic distance (R12). This will allow extremely high accuracy to be achieved while dramatically reducing the number of basis functions needed to describe the electron–electron correlation cusp and, thus, dramatically reducing the computational costs, which typically depend on the number of basis functions to the fifth or higher power. Algorithms and software will be developed for several correlation schemes including MP perturbation theory, coupled cluster theory, and Brueckner theory. www.osti.gov /scidac/bes/projects/schaefer.html   (166 words)

 [No title]   (Site not responding. Last check: 2007-10-08) Gwaltney and M. Head-Gordon, "A Second Order Correction to Singles and Doubles Coupled Cluster Methods Based on a Perturbative Expansion of a Similarity-Transformed Hamiltonian", Chem. Gwaltney, C. Sherrill, M. Head-Gordon, and A. Krylov, "Second Order Perturbation Corrections to Singles and Doubles Coupled Cluster Methods: General Theory and Application to the Valence Optimized Doubles Model", J. Van Voorhis and M. Head-Gordon, "The Quadratic Coupled Cluster Doubles Model", Chem. www.q-chem.com /tech/mp2_wav_cit.html   (332 words)

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