Minimum Energy Path Calculations Research Articles

Role of transition metal oxides in metal dusting: Density functional study

AbstractDensity function theory was applied to study the mechanisms and energetics of two major metal dusting processes represented by Boudouard and steam‐carbon reactions on the FeO(100) surface. Cluster models were utilized to represent the surface. The chosen cluster model was validated by examining CO adsorption binding energies on clusters of various sizes. We show that the lattice relaxation has a relatively small effect on the adsorption. The reaction process involving direct abstraction of O from the surface by CO was excluded from consideration of the overall dusting processes due to unfavorable energetics. Minimum energy path calculations were carried out to investigate the reaction mechanisms. It was found that both the Boudouard and steam‐carbon reactions are thermochemically and kinetically unfavorable on transition metal oxide surfaces. Detailed insight into the reaction mechanisms was obtained by following the reaction trajectories and analyzing the electron population distribution along the reaction paths. This study elucidates the empirical observation that metal oxide can often minimize metal dusting.

The MaxFlux algorithm for calculating variationally optimized reaction paths for conformational transitions in many body systems at finite temperature

An algorithm for the calculation of reaction paths between known reactant and product states in systems of low or high dimension is described. The optimal reaction path is defined as the path of maximum flux for a diffusive dynamics assuming isotropic friction. The resulting reaction path is temperature dependent and independent of the magnitude of the friction. Comparison is made with a number of algorithms designed for the calculation of minimum-energy reaction paths. Applications to two model potentials and an extended atom model of a dipeptide are presented. The applications demonstrate the ability of the algorithm to isolate a temperature-dependent optimal reaction path for a high dimensional molecular system.

A theoretical study of the intramolecular solvolytic mechanism of the Meyer–Schuster reaction. MINDO/3 and CNDO/2 calculations of minimum energy paths

Theoretical results give strong support to an intramolecular solvolytic mechanism for the Meyer–Schuster rearrangement. Both CNDO/2 and MINDO/3 reaction paths suggest that the possibility of a 1,3 propargylic shift across the triple bond in a model α-acetylenic tertiary alcohol can be discarded. The electronic structure of the reaction intermediate corresponds to an alkynyl cation interacting electrostatically with a water molecule. For non-aqueous solvents this result agrees with the formation of a stable alkynyl carbocation, which has been found experimentally. For aqueous solvents the nature of the reaction path leads to the conclusion that the intermolecular mechanism which has been proposed for this reaction is more realistic.

Quantum-chemical studies of the energy hypersurface for the Meyer—Schuster rearrangement STO-3G calculation of minimum-energy paths. Intermolecular mechanism

Minimum-energy (ME) paths have been calculated for an intermolecular mechanism of the acid-catalysed rearrangement of α-acetylenic tertiary alcohols. Hydrogen-bonding along the reaction path is examined. A detailed characterization of the saddle point has been obtained. Good agreement between calculated and experimental activation enthalpy is found. The hypersurface obtained here points out a possible major role of solvation along the ME reaction path.