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Ab Initio Calculation of Rate Constants for Molecule-Surface Reactions with Chemical Accuracy.

Piccini G, Alessio M, Sauer J - Angew. Chem. Int. Ed. Engl. (2016)

Bottom Line: We present a divide-and-conquer strategy that departs from the potential energy surfaces obtained by standard density functional theory with inclusion of dispersion.The energies of the reactant and transition structures are refined by wavefunction-type calculations for the reaction site.Thermal effects and entropies are calculated from vibrational partition functions, and the anharmonic frequencies are calculated separately for each vibrational mode.

View Article: PubMed Central - PubMed

Affiliation: Institut für Chemie, Humboldt-Universität, Unter den Linden 6, 10099, Berlin, Germany.

No MeSH data available.


Logarithm of the observed/calculated ratios for the rate constants (left) and pre‐exponentials (right). “Anharm‐Hybrid” and “Harm‐Hybrid” refer to results calculated with anharmonic and harmonic frequencies, respectively, whereas “Harm‐Svelle” refers to harmonic frequencies obtained for a part of the system.1 The “Harm‐VanSp” results5 were obtained with a 46 tetrahedra cluster model. The gray region represents a deviation of ±1 order of magnitude from the observed values.
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anie201601534-fig-0003: Logarithm of the observed/calculated ratios for the rate constants (left) and pre‐exponentials (right). “Anharm‐Hybrid” and “Harm‐Hybrid” refer to results calculated with anharmonic and harmonic frequencies, respectively, whereas “Harm‐Svelle” refers to harmonic frequencies obtained for a part of the system.1 The “Harm‐VanSp” results5 were obtained with a 46 tetrahedra cluster model. The gray region represents a deviation of ±1 order of magnitude from the observed values.

Mentions: Figure 2 and Figure 3 show the results for the enthalpy barriers, the pre‐exponentials, and the rate constants as a function of the alkene length at a pressure of 10−4 MPa and a temperature of 623 K. The labels “Anharm‐Hybrid” and “Harm‐Hybrid” refer to the anharmonic and harmonic vibrational energies, respectively, which were obtained by using finite‐difference normal‐mode distortions in internal coordinate representation.17 Comparison will also be made with previous results of Svelle and co‐workers,1 which differ from the present one in the following respect: In Svelle's report, the structures had been optimized and the harmonic frequencies had been calculated with PBE without including dispersion, whereas in the present study, PBE+D2 was used. Moreover, Svelle et al. used finite differences of Cartesian distortions to obtain the harmonic force constants and limited this to some of the atoms of the whole system (“partial Hessian”), whereas in the present study, the anharmonic and harmonic frequencies were calculated including all atoms. Unlike Svelle et al., who used a two‐point formula for the finite difference, the harmonic force constants of the present work were obtained from finite differences using all eight points of the curvilinear sampling of the normal mode.17


Ab Initio Calculation of Rate Constants for Molecule-Surface Reactions with Chemical Accuracy.

Piccini G, Alessio M, Sauer J - Angew. Chem. Int. Ed. Engl. (2016)

Logarithm of the observed/calculated ratios for the rate constants (left) and pre‐exponentials (right). “Anharm‐Hybrid” and “Harm‐Hybrid” refer to results calculated with anharmonic and harmonic frequencies, respectively, whereas “Harm‐Svelle” refers to harmonic frequencies obtained for a part of the system.1 The “Harm‐VanSp” results5 were obtained with a 46 tetrahedra cluster model. The gray region represents a deviation of ±1 order of magnitude from the observed values.
© Copyright Policy - creativeCommonsBy-nc-nd
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4834608&req=5

anie201601534-fig-0003: Logarithm of the observed/calculated ratios for the rate constants (left) and pre‐exponentials (right). “Anharm‐Hybrid” and “Harm‐Hybrid” refer to results calculated with anharmonic and harmonic frequencies, respectively, whereas “Harm‐Svelle” refers to harmonic frequencies obtained for a part of the system.1 The “Harm‐VanSp” results5 were obtained with a 46 tetrahedra cluster model. The gray region represents a deviation of ±1 order of magnitude from the observed values.
Mentions: Figure 2 and Figure 3 show the results for the enthalpy barriers, the pre‐exponentials, and the rate constants as a function of the alkene length at a pressure of 10−4 MPa and a temperature of 623 K. The labels “Anharm‐Hybrid” and “Harm‐Hybrid” refer to the anharmonic and harmonic vibrational energies, respectively, which were obtained by using finite‐difference normal‐mode distortions in internal coordinate representation.17 Comparison will also be made with previous results of Svelle and co‐workers,1 which differ from the present one in the following respect: In Svelle's report, the structures had been optimized and the harmonic frequencies had been calculated with PBE without including dispersion, whereas in the present study, PBE+D2 was used. Moreover, Svelle et al. used finite differences of Cartesian distortions to obtain the harmonic force constants and limited this to some of the atoms of the whole system (“partial Hessian”), whereas in the present study, the anharmonic and harmonic frequencies were calculated including all atoms. Unlike Svelle et al., who used a two‐point formula for the finite difference, the harmonic force constants of the present work were obtained from finite differences using all eight points of the curvilinear sampling of the normal mode.17

Bottom Line: We present a divide-and-conquer strategy that departs from the potential energy surfaces obtained by standard density functional theory with inclusion of dispersion.The energies of the reactant and transition structures are refined by wavefunction-type calculations for the reaction site.Thermal effects and entropies are calculated from vibrational partition functions, and the anharmonic frequencies are calculated separately for each vibrational mode.

View Article: PubMed Central - PubMed

Affiliation: Institut für Chemie, Humboldt-Universität, Unter den Linden 6, 10099, Berlin, Germany.

No MeSH data available.