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1 2001

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Modelowanie oddziaływania wodoru z metalami przejściowymi za pomocą teorii funkcjonałów gęstości (DFT). Perspektywa kwantowych modeli katalizy heterogenicznej

Bartczak W.M., Romanowski S., Łandwijt M.

Wiadomości Chemiczne

2001

[Z] 55, 7-8

629-655

Computer modelling of catalytic effects of a series of the transition metals and their alloys on the process of dissociation of molecular hydrogen has been performed. The project was composed of three stages. First, the binding energy versus the internuclear distance has been calculated for a series of metal dimers and mixed dimers: Ni2, NiCu, Cu2, Ag2, AgPd, Pd2 Au2, Pt2, AuPt. It has been shown that the traditional methods of quantum chemistry: the ZINDO semiempirical methods and the Hartree-Fock methods do not work properly in the case of the transition metal dimers. In contrast with these methods, the calculations based on the nonlocal version of the density functional theory (DFT) provide very good results, in full agreement with available experimental data concerning the dissociation energies and equilibrium bond lengths of the metal dimers. Then, using the fitted Morse form of the potential interaction between the metal atoms, the Molecular Dynamics (MD) simulations have been performed in order to obtain the atomic structures appearing in the alloys. The third part of the project includes the quantum-chemical calculations of hydrogen atom and hydrogen molecule positioned over the metallic dimers. The interatomic distances of the dimers were taken from the MD calculations. A range of the distances of hydrogen from the metal dimers was scanned. The evolution of energy and electron density with the hydrogen distance from certain dimers, like NiCu, AgPd and Pd2, clearly exhibits the process of the hydrogen molecule dissociation. On a basis of these calculations a measure of catalytic power of the metals was defined and the series of metals and alloys was ordered according to their catalytic power. It was found that the highest catalytic power with respect to the hydrogen dissociation process is exhibited by NiCu alloys. All the quantum-chemical calculations have been performed using the methods of the Density Functional Theory. The nonlocal version of the DFT was applied with the gradient-corrected hybrid functionals for electron exchange and correlation. The GAUSSIAN 98 suite of programs was employed in the calculations.