Gaussian-3 theory using coupled cluster energies

Curtiss, Larry A.; Raghavachari, Krishnan; Redfern, Paul C.; Baboul, Anwar G.; Pople, John A.

doi:10.1016/s0009-2614(99)01126-4

Cited by 226 publications

(203 citation statements)

References 22 publications

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“…For the homologue series, (CH 2 ) n chains were kept in the extended conformations, while full conformational searches at a resolution of 60° were performed for all other species in the present work. Accurate electronic energies were calculated using a variety of methods ranging from DFT and MP2 to high-level composite G3(MP2)RAD, 35 G3(MP2,CC) 36 and G4(MP2)-6X 37 procedures. Calculations on radicals were performed with an unrestricted wave function except in cases designated with an "R" prefix where a restricted open-shell wave function was used.…”

Section: Discussionmentioning

confidence: 99%

Switching radical stability by pH-induced orbital conversion

et al. 2013

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In most radicals the singly occupied molecular orbital (SOMO) is the highest-energy occupied molecular orbital (HOMO); however, in a small number of reported compounds this is not the case. In the present work we expand significantly the scope of this phenomenon, known as SOMO-HOMO energy-level conversion, by showing that it occurs in virtually any distonic radical anion that contains a sufficiently stabilized radical (aminoxyl, peroxyl, aminyl) non-π-conjugated with a negative charge (carboxylate, phosphate, sulfate). Moreover, regular orbital order is restored on protonation of the anionic fragment, and hence the orbital configuration can be switched by pH. Most importantly, our theoretical and experimental results reveal a dramatically higher radical stability and proton acidity of such distonic radical anions. Changing radical stability by 3-4 orders of magnitude using pH-induced orbital conversion opens a variety of attractive industrial applications, including pH-switchable nitroxide-mediated polymerization, and it might be exploited in nature. AbstractIn most radicals the singly-occupied molecular orbital (SOMO) is the highest-energy occupied one

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Section: Discussionmentioning

confidence: 99%

Switching radical stability by pH-induced orbital conversion

et al. 2013

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“…The same method was used to obtain vibrational frequencies, molecular structural parameters, zeropoint energy (ZPE) corrections, and to characterize the stationary points as minima or first-order saddle points. To obtain more accurate energies, we applied the G3(MP2,CC)//B3LYP modification (52,53) of the original Gaussian 3 (G3) scheme (54) for high-level single-point energy calculations. The final energies at 0 K were obtained using the B3LYP optimized geometries and ZPE corrections according to the following formula E 0 ½G3ðMP2;CCÞ ¼ E½CCSDðT Þ∕6-311Gðd;pÞ þ ΔE MP2 þ EðZPEÞ, where ΔE MP2 ¼ E½MP2∕G3large− E½MP2∕6-311Gðd;pÞ is the basis set correction and E(ZPE) is the zero-point energy.…”

Section: Methodsmentioning

confidence: 99%

Low temperature formation of naphthalene and its role in the synthesis of PAHs (Polycyclic Aromatic Hydrocarbons) in the interstellar medium

Parker

Zhang

Kim

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

207

156

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Polycyclic aromatic hydrocarbons (PAHs) are regarded as key molecules in the astrochemical evolution of the interstellar medium, but the formation mechanism of even their simplest prototypenaphthalene (C 10 H 8 )-has remained an open question. Here, we show in a combined crossed beam and theoretical study that naphthalene can be formed in the gas phase via a barrierless and exoergic reaction between the phenyl radical (C 6 H 5 ) and vinylacetylene (CH 2 CH-C ≡ CH) involving a van-der-Waals complex and submerged barrier in the entrance channel. Our finding challenges conventional wisdom that PAH-formation only occurs at high temperatures such as in combustion systems and implies that low temperature chemistry can initiate the synthesis of the very first PAH in the interstellar medium. In cold molecular clouds, barrierless phenyl-type radical reactions could propagate the vinylacetylenemediated formation of PAHs leading to more complex structures like phenanthrene and anthracene at temperatures down to 10 K.astrochemistry | reaction dynamics | molecular beams | flame chemistry

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“…Compared to the G1 method, two important additive corrections were included in the G3 energies, core-valence correlation and atomic spin-orbit splitting. Fur-ther modifications to the G3 method have included reducing the basis set size, 13 employing coupled cluster computations with single, double, and perturbative triple excitations ͓CCSD͑T͔͒ instead of quadratic configuration interaction ͓QCISD͑T͔͒ to create the G3͑CC͒ variant, 14,15 using B3LYP density functional theory ͑DFT͒ equilibrium geometries and vibrational frequencies ͑G3B and G3X͒, 16,17 using second-or third-order MPn theory instead of MP4 to determine the reference electronic energy ͓G3͑MP2͒ and G3͑MP3͔͒, 18,19 and using scale factors to replace the HLC ͑G3S and G3SX͒. 17,20 Besides the Gn methods, other composite approaches have been introduced.…”

Section: Introductionmentioning

confidence: 99%

The correlation-consistent composite approach: Application to the G3/99 test set

DeYonker

Grimes

Yockel

et al. 2006

The Journal of Chemical Physics

148

167

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The correlation-consistent composite approach ͑ccCA͒, an ab initio composite technique for computing atomic and molecular energies, recently has been shown to successfully reproduce experimental data for a number of systems. The ccCA is applied to the G3/99 test set, which includes 223 enthalpies of formation, 88 adiabatic ionization potentials, 58 adiabatic electron affinities, and 8 adiabatic proton affinities. Improvements on the original ccCA formalism include replacing the small basis set quadratic configuration interaction computation with a coupled cluster computation, employing a correction for scalar relativistic effects, utilizing the tight-d forms of the second-row correlation-consistent basis sets, and revisiting the basis set chosen for geometry optimization. With two types of complete basis set extrapolation of MP2 energies, ccCA results in an almost zero mean deviation for the G3/99 set ͑with a best value of −0.10 kcal mol −1 ͒, and a 0.96 kcal mol −1 mean absolute deviation, which is equivalent to the accuracy of the G3X model chemistry. There are no optimized or empirical parameters included in the computation of ccCA energies. Except for a few systems to be discussed, ccCA performs as well as or better than Gn methods for most systems containing first-row atoms, while for systems containing second-row atoms, ccCA is an improvement over Gn model chemistries.

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Gaussian-3 theory using coupled cluster energies

Cited by 226 publications

References 22 publications

Switching radical stability by pH-induced orbital conversion

Switching radical stability by pH-induced orbital conversion

Low temperature formation of naphthalene and its role in the synthesis of PAHs (Polycyclic Aromatic Hydrocarbons) in the interstellar medium

The correlation-consistent composite approach: Application to the G3/99 test set

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