Heats of formation of organic molecules. 2. The basis for calculations using either ab initio or molecular mechanics methods. Alcohols and ethers

Allinger, Norman L.; Schmitz, Lawrence R.; Mot̨oc, Ioan; Bender, Charles F.; Labanowski, Jan K.

doi:10.1021/ja00034a019

Cited by 66 publications

(55 citation statements)

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“…[8][9][10][11][12][13][14][15] Briefly, it consists of calculating an energy using Hartree-Fock or density functional theory, and converting it to a heat of formation using bond and group equivalents and statistical mechanical terms. It can be summarized in the equation:…”

Section: Methodsmentioning

confidence: 99%

Heats of formation of organic molecules calculated by density functional theory. III?Amines

Schmitz

Chen

Labanowski

et al. 2001

J. Phys. Org. Chem.

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Section: Methodsmentioning

confidence: 99%

Heats of formation of organic molecules calculated by density functional theory. III?Amines

Schmitz

Chen

Labanowski

et al. 2001

J. Phys. Org. Chem.

Self Cite

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“…The atom-additivity was intuitively presumed and was posteriori justified in terms of the repeated success in predicting D f H o by many variants of the above scheme. [24][25][26][29][30][31] Explicitly retaining the terms associated with vibrational energy and other temperature-dependent contributions may not achieve much unless very high levels of theory are used. Also, given the significantly greater computational cost of evaluating the vibrational frequencies, these terms like other implicit deficiencies in theory may be lumped in the empirical atomic correction terms to be estimated using reliable experimental D f H o data for a small representative ''training'' set of molecules.…”

Section: Introductionmentioning

confidence: 99%

“…Repasky et al 31 used the scheme popularized by Allinger et al 24 , 61 bond and group equivalents of the same lineage and computationally less demanding semiempirical methods for energy computation. For a set of 583 neutral, closed-shell molecules containing carbon, hydrogen, nitrogen and oxygen the MAD was found to be 9.6, 9.2 and 12.5 kJ/mol for the AM1, PM3 and MNDO methods, respectively.…”

Section: Introductionmentioning

confidence: 99%

Converting ab initio energies to enthalpies of formation of free radicals. I. New atom equivalents for alkyl radicals

Bhattacharya¹

2011

AIChE Journal

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A simple method is presented to convert ab initio computed total energies to the standard enthalpy of formation (D f H o ) of a large number of saturated alkyl radicals (especially those that are relatively highly branched), for which experimental data are scarcely available. For this purpose a new set of radical atom-equivalents (AEQ) and their unique combinations were defined and the energy values of the latter assigned. The theory level and the basis set requirement for the quantum chemistry calculation of the molecular energy were found to be moderate. The D f H o predictions appear to be quite accurate with reference to limited available experimental data and are better than values calculated by the group-additivity and the difference methods. The strategy provides an inexpensive way of harnessing the power of computational chemistry and combining it with the organization and insight from the group-additivity method sans any empirical corrections.

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“…[38][39][40][41][42][43][44] The atomic equivalents (AEs) and group equivalents (GEs) approaches, which are originated from the same concept, have been explored by several research groups. [45][46][47][48] Though AE and GE predictions are more accurate than those obtained from atomization and isodesmic or homodesmic reactions, their accuracies are still less than satisfactory. [49] Besides, deficiencies of DFT in describing the protobranching stabilization are still there, as these methods simply ' 'translate' ' the computed enthalpies into predicted enthalpies of formation via the optimized equivalents.…”

Section: Introductionmentioning

confidence: 99%

Accurate prediction of the enthalpies of formation for xanthophylls

Lii

Liao

2011

J Comput Chem

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This study investigates the applications of computational approaches in the prediction of enthalpies of formation (ΔH(f)) for C-, H-, and O-containing compounds. Molecular mechanics (MM4) molecular mechanics method, density functional theory (DFT) combined with the atomic equivalent (AE) and group equivalent (GE) schemes, and DFT-based correlation corrected atomization (CCAZ) were used. We emphasized on the application to xanthophylls, C-, H-, and O-containing carotenoids which consist of ∼ 100 atoms and extended π-delocaization systems. Within the training set, MM4 predictions are more accurate than those obtained using AE and GE; however a systematic underestimation was observed in the extended systems. ΔH(f) for the training set molecules predicted by CCAZ combined with DFT are in very good agreement with the G3 results. The average absolute deviations (AADs) of CCAZ combined with B3LYP and MPWB1K are 0.38 and 0.53 kcal/mol compared with the G3 data, and are 0.74 and 0.69 kcal/mol compared with the available experimental data, respectively. Consistency of the CCAZ approach for the selected xanthophylls is revealed by the AAD of 2.68 kcal/mol between B3LYP-CCAZ and MPWB1K-CCAZ.

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Heats of formation of organic molecules. 2. The basis for calculations using either ab initio or molecular mechanics methods. Alcohols and ethers

Cited by 66 publications

References 0 publications

Heats of formation of organic molecules calculated by density functional theory. III?Amines

Heats of formation of organic molecules calculated by density functional theory. III?Amines

Converting ab initio energies to enthalpies of formation of free radicals. I. New atom equivalents for alkyl radicals

Accurate prediction of the enthalpies of formation for xanthophylls

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