Grupo uakti

Ribeiro, Artur Andrés

doi:10.1590/s0103-40142000000200016

Cited by 1 publication

(3 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As the frequency tends towards zero, the logarithmic term in this equation diverges, meaning that numerical noise in calculating low vibrational modes can greatly influence the computed entropy values. 56 Furthermore, low frequency free or hindered internal rotations are inherently poorly described by a harmonic approximation. The adoption of quasi-RRHO approaches, in which entropic terms associated with low frequencies are computed outside of the RRHO paradigm, have recently been suggested for improved estimates of thermochemical quantities by Truhlar, 56,57 Grimme, 22 and Head-Gordon.…”

Section: Thermal Corrections To the Gibbs Energymentioning

confidence: 99%

“…56 Furthermore, low frequency free or hindered internal rotations are inherently poorly described by a harmonic approximation. The adoption of quasi-RRHO approaches, in which entropic terms associated with low frequencies are computed outside of the RRHO paradigm, have recently been suggested for improved estimates of thermochemical quantities by Truhlar, 56,57 Grimme, 22 and Head-Gordon. 58 Quasi-RRHO corrections are typically a few percent of the total thermal correction, and so are larger in absolute terms (i.e.…”

Section: Thermal Corrections To the Gibbs Energymentioning

confidence: 99%

“…We found uniformly better performance using this quasi-RRHO treatment than from simply transposing low frequencies to higher wavenumbers as also used in quasi-harmonic corrections in the literature. 56 This method is seen to be universally worse when compared to Grimme as it depends largely upon the number of low frequency modes for each conformer, and deteriorates for larger cut-off values.…”

mentioning

confidence: 97%

See 2 more Smart Citations

Hydrogen-Bond-Dependent Conformational Switching: A Computational Challenge from Experimental Thermochemistry

Luccarelli

Paton

2018

J. Org. Chem.

View full text Add to dashboard Cite

We have compiled an experimental dataset (SWITCH10) of equilibrium constants for a series of hydrogen-bond dependent conformational switches. These organic molecules possess common functionalities and are representative in terms of size and composition of systems routinely studied computationally. They exist as two well-defined conformations which serve as a useful tool to benchmark computational estimates of experimental Gibbs energy differences. We examine the performance of HF theory and a variety of density functionals (B3LYP, B3LYP-D3, CAM-B3LYP, ωB97X-D, M06-2X) against these experimental benchmarks. Surprisingly, despite a strong similarity between the two switch conformations, the average errors (0.4 -1.7 kcal mol −1 ) obtained across the dataset for all methods are larger than obtained with HF calculations. B3LYP was found to outperform implicitly and explicitly-dispersion corrected functionals, with an average error smaller by 1 kcal mol −1 . Unsystematic errors in the optimized structures were found to contribute to the relatively poor performance obtained, while quasi-rigid rotor harmonic oscillator thermal contributions are important in improving the accuracy of computed Gibbs energy differences. These results emphasize the challenge of quantitative accuracy in computing solution-phase thermochemistry for flexible systems and caution against the often used (but unstated) assumption of favorable error cancellation in comparing conformers or stereoisomers.

show abstract