A Novel Approach to Parallel Coupled Cluster Calculations:  Combining Distributed and Shared Memory Techniques for Modern Cluster Based Systems

Olson, Ryan M.; Bentz, Jonathan L.; Kendall, Ricky A.; Schmidt, Michael W.; Gordon, Mark S.

doi:10.1021/ct600366k

Cited by 120 publications

(140 citation statements)

References 61 publications

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“…They found that CCSD(T) predicted the relative energy spacings to be slightly larger than MP2 but that both methods predicted the same energy ordering. We note that MP2 is commonly used 6,[43][44][45] for benchmark energies of water oligimers when CCSD(T) is too expensive, but in the present case, we used new state-of-the-art capabilities 42 to calculate benchmark results at the higher CCSD(T) level.…”

Section: Introductionmentioning

confidence: 99%

Assessment of the Accuracy of Density Functionals for Prediction of Relative Energies and Geometries of Low-Lying Isomers of Water Hexamers

et al. 2008

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Water hexamers provide a critical testing ground for validating potential energy surface predictions because they contain structural motifs not present in smaller clusters. We tested the ability of 11 density functionals (four of which are local and seven of which are nonlocal) to accurately predict the relative energies of a series of low-lying water hexamers, relative to the CCSD(T)/aug′-cc-pVTZ level of theory, where CCSD(T) denotes coupled cluster theory with an interative treatment of single and double excitations and a quasiperturbative treatment of connected triple excitations. Five of the density functionals were tested with two different basis sets, making a total of 16 levels of density functional theory (DFT) tested. When single-point energy calculations are carried out on geometries obtained with second-order Møller-Plesset perturbation theory (MP2), only three density functionals, M06-L, M05-2X, and M06-2X, are able to correctly predict the relative energy ordering of the hexamers. These three functionals predict that the range of energies spanned by the six isomers is 3.2-5.6 kcal/mol, whereas the other eight functionals predict ranges of 1.0-2.4 kcal/ mol; the benchmark value for this range is 3.1 kcal/mol. When the hexamers are optimized at each level of theory, all methods are able to reproduce the MP2 geometries well for all isomers except the boat and bag isomers, and DFT optimization changes the energy ordering for seven of the 16 methods tested. The addition of zero-point energy changes the energy ordering for all of the density functionals studied except for M05-2X and M06-2X. The variation in relative energies predicted by the different methods highlights the necessity for exercising caution in the choice of density functionals used in future studies. Of the 11 density functionals tested, the most accurate results for energies were obtained with the PWB6K, MPWB1K, and M05-2X functionals.

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Section: Introductionmentioning

confidence: 99%

Assessment of the Accuracy of Density Functionals for Prediction of Relative Energies and Geometries of Low-Lying Isomers of Water Hexamers

et al. 2008

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“…2͔͒ are very distinct and close to each other and to earlier CCSD͑T͒ results. 16 These trends cannot be accounted for by DFT with traditional GGA ͓PBE ͑Ref. 17͒, RPBE ͑Ref.…”

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Density functional for van der Waals forces accounts for hydrogen bond in benchmark set of water hexamers

Kelkkanen

Lundqvist

Nørskov

2009

The Journal of Chemical Physics

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A recent extensive study has investigated how various exchange-correlation (XC) functionals treat hydrogen bonds in water hexamers and has shown traditional generalized gradient approximation and hybrid functionals used in density-functional (DF) theory to give the wrong dissociation-energy trend of low-lying isomers and van der Waals (vdW) dispersion forces to give key contributions to the dissociation energy. The question raised whether functionals that incorporate vdW forces implicitly into the XC functional predict the correct lowest-energy structure for the water hexamer and yield accurate total dissociation energy is here answered affirmatively for the vdW-DF [M. Dion et al., Phys. Rev. Lett.92, 246401 (2004)].

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“…Energies for all species are presented using closed or spin-restricted open shell MP2 [10,11]. For singlets, a parallel CCSD(T) program [107] could be used to check the MP2 results. CCSD(T) energies, where available, are given in parentheses after the MP2 energies.…”

Section: A Methodsmentioning

confidence: 99%

The Decomposition of Hydrazine in the Gas Phase and over an Iridium Catalyst

Schmidt

Gordon

2013

Zeitschrift Für Physikalische Chemie

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Hydrazine / Gas Phase / Ir Catalyst / Quantum ChemistryHydrazine is an important rocket fuel, used as both a monopropellant and a bipropellant. This paper presents theoretical results to complement the extensive experimental studies of the gas phase and Ir catalyzed decompositions involved in the monopropellant applications of hydrazine. Gas phase electronic structure theory calculations that include electron correlation predict that numerous molecular and free radical reactions occur within the same energy range as the basic free radical pathways: NN bond breaking around 65 kcal/mol and NH bond breaking around 81 kcal/mol. The data suggest that a revision to existing kinetics modeling is desirable, based on the energetics and the new elementary steps reported herein. A supported Ir 6 octahedron model for the Shell 405 Iridium catalyst used in thrusters was developed. Self-Consistent Field and electron correlation calculations (with core potentials and associated basis sets) find a rich chemistry for hydrazine on this catalyst model. The model catalyst provides dramatically lower NN and NH bond cleavage energies and an even smaller barrier to breaking the NH bond by NH 2 abstractions. Thus, the low temperature decomposition over the catalyst is interpreted in terms of consecutive NH 2 abstractions to produce ammonia and nitrogen. The higher temperature channel, which has hydrogen and nitrogen products, may be due to a mixture of two mechanisms. These two mechanisms are successive NH cleavages with surface H + H recombinations, and the same type of assisted H 2 eliminations found to occur in the gas phase part of this study.

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A Novel Approach to Parallel Coupled Cluster Calculations: Combining Distributed and Shared Memory Techniques for Modern Cluster Based Systems

Cited by 120 publications

References 61 publications

Assessment of the Accuracy of Density Functionals for Prediction of Relative Energies and Geometries of Low-Lying Isomers of Water Hexamers

Assessment of the Accuracy of Density Functionals for Prediction of Relative Energies and Geometries of Low-Lying Isomers of Water Hexamers

Density functional for van der Waals forces accounts for hydrogen bond in benchmark set of water hexamers

The Decomposition of Hydrazine in the Gas Phase and over an Iridium Catalyst

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