HEAT: High accuracy extrapolated <i>ab initio</i> thermochemistry

Tajti, Attila; Szalay, Péter G.; Császár, Attila G.; Kállay, Mihály; Gauß, Jürgen; Valeev, Edward F.; Flowers, B. A.; Vázquez, Juana; Stanton, John F.

doi:10.1063/1.1811608

Cited by 762 publications

(844 citation statements)

References 77 publications

(36 reference statements)

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“…Specifically, the effects of valence electron correlation have been included up to the coupled-cluster singles, doubles, triples and quadruples (CCSDTQ) level of theory, using the equation-of-motion (EOM) variant of coupled-cluster theory to treat these excited state isomers. In addition, effects of basis set insufficiency are estimated using extrapolation techniques 49 , and contributions due to zero point energies, core correlation and scalar relativistic effects are included as well. The final result of these calculations predicts the zero-point level of the cis isomer to lie at 44861 cm −1 , a calculation that we believe to be in error by no more than 50 cm −1 .…”

Section: A2 Cis Statesmentioning

confidence: 99%

Reduced dimension discrete variable representation study of cis–trans isomerization in the S1 state of C2H2

Baraban

Beck

Steeves

et al. 2011

The Journal of Chemical Physics

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Isomerization between the cis and trans conformers of the S 1 state of acetylene is studied using a reduced dimension DVR calculation. Existing DVR techniques are combined with a high accuracy potential energy surface and a kinetic energy operator derived from FG theory to yield an effective but simple Hamiltonian for treating large amplitude motions. The spectroscopic signatures of the S 1 isomerization are discussed, with emphasis on the vibrational aspects. The presence of a low barrier to isomerization causes distortion of the trans vibrational level structure and the appearance of nominally electronically forbiddenÃ 1 A 2 ←X 1 Σ + g transitions to vibrational levels of the cis conformer. Both of these effects are modeled in agreement with experimental results, and the underlying mechanisms of tunneling and state mixing are elucidated by use of the calculated vibrational wavefunctions.

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Section: A2 Cis Statesmentioning

confidence: 99%

Reduced dimension discrete variable representation study of cis–trans isomerization in the S1 state of C2H2

Baraban

Beck

Steeves

et al. 2011

The Journal of Chemical Physics

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“…7,46 This chemical kinetics analysis is performed using a high accuracy potential energy surface that is constructed with a modification of the HEAT protocol. [47][48][49] In addition, we investigate the fate of vinyl hydrogen peroxide (VHP), which was recently detected as an intermediate in a carboxylic acid-catalyzed tautomerization study of syn-CH 3 CHOO. 50 …”

Section: Introductionmentioning

confidence: 99%

Communication: Thermal unimolecular decomposition of syn-CH3CHOO: A kinetic study

Nguyen

McCaslin

McCarthy

et al. 2016

The Journal of Chemical Physics

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The thermal decomposition of syn-ethanal-oxide (syn-CH 3 CHOO) through vinyl hydrogen peroxide (VHP) leading to hydroxyl radical is characterized using a modification of the HEAT thermochemical protocol. The isomerization step of syn-CH 3 CHOO to VHP via a 1,4 H-shift, which involves a moderate barrier of 72 kJ/mol, is found to be rate determining. A two-dimensional master equation approach, in combination with semi-classical transition state theory, is employed to calculate the time evolution of various species as well as to obtain phenomenological rate coefficients. This work suggests that, under boundary layer conditions in the atmosphere, thermal unimolecular decomposition is the most important sink of syn-CH 3 CHOO. Thus, the title reaction should be included into atmospheric modeling. The fate of cold VHP, the intermediate stabilized by collisions with a third body, has also been investigated. Published by AIP Publishing. [http://dx

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“…1 Coupled-cluster theory entails a hierarchy of approximations that can be systematically improved towards the exact quantum mechanical solution, providing a roadmap for highly accurate chemical properties. [2][3][4][5][6][7][8] In particular, the CCSD(T) method (coupled-cluster with single, double, and quasiperturbative triple excitations) has been found to be a cost-effective approach for the calculation of reliable thermochemical and kinetic data(e.g. reaction energies and barrier heights) as well as molecular properties based on energy derivatives (e.g.…”

Section: Introductionmentioning

confidence: 99%

Estimating the CCSD basis-set limit energy from small basis sets: basis-set extrapolations vs additivity schemes

Spackman

Karton

2015

AIP Advances

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Coupled cluster calculations with all single and double excitations (CCSD) converge exceedingly slowly with the size of the one-particle basis set. We assess the performance of a number of approaches for obtaining CCSD correlation energies close to the complete basis-set limit in conjunction with relatively small DZ and TZ basis sets. These include global and system-dependent extrapolations based on the A + B/L α two-point extrapolation formula, and the well-known additivity approach that uses an MP2-based basis-set-correction term. We show that the basis set convergence rate can change dramatically between different systems(e.g.it is slower for molecules with polar bonds and/or second-row elements). The system-dependent basis-set extrapolation scheme, in which unique basis-set extrapolation exponents for each system are obtained from lower-cost MP2 calculations, significantly accelerates the basis-set convergence relative to the global extrapolations. Nevertheless, we find that the simple MP2-based basis-set additivity scheme outperforms the extrapolation approaches. For example, the following root-mean-squared deviations are obtained for the 140 basis-set limit CCSD atomization energies in the W4-11 database: 9.1 (global extrapolation), 3.7 (system-dependent extrapolation), and 2.4 (additivity scheme) kJ mol -1 . The CCSD energy in these approximations is obtained from basis sets of up to TZ quality and the latter two approaches require additional MP2 calculations with basis sets of up to QZ quality. We also assess the performance of the basis-set extrapolations and additivity schemes for a set of 20 basis-set limit CCSD atomization energies of larger molecules including amino acids, DNA/RNA bases, aromatic compounds, and platonic hydrocarbon cages. We obtain the following RMSDs for the above methods: 10.2 (global extrapolation), 5.7 (system-dependent extrapolation), and 2.9 (additivity scheme) kJ mol -1 . C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx

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HEAT: High accuracy extrapolated ab initio thermochemistry

Cited by 762 publications

References 77 publications

Reduced dimension discrete variable representation study of cis–trans isomerization in the S1 state of C2H2

Reduced dimension discrete variable representation study of cis–trans isomerization in the S1 state of C2H2

Communication: Thermal unimolecular decomposition of syn-CH3CHOO: A kinetic study

Estimating the CCSD basis-set limit energy from small basis sets: basis-set extrapolations vs additivity schemes

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