Modified Shepard interpolation method applied to trapping mediated adsorption dynamics

P. N. ABUFAGER; C. CRESPOS; H. F. BUSNENGO

Cuernavaca, Mexico

Conferencia; The fourth San Luis Summer School and Conference on Surfaces, Interfaces and Catalysis; 2007

Nowadays molecule-surface interactions are theoretically studied through the analysis of the corresponding potential energy surface (PES) obtained, in general, from state-of-the-art electronic structure calculations based on Density Functional Theory (DFT). Due to their computational cost, these calculations are carried out for some selected molecular configurations considered as the most relevant ones for the process of interest. However, dynamic simulations require values of the potential and forces for a great number of molecular configurations. Therefore, an accurate continuous representation of the PES obtained by interpolation or fitting of a reduced set of DFT data is highly desirable. Thus, in the last decade, various interpolation and fitting methods have been proposed and implemented for both gas phase and molecules-surface reactions. Recently, the Modified Shepard (MS) interpolation developed in the framework of gas phase reactions [1,2] was adapted to the problem of diatomic molecules reacting on surfaces [3]. The key point involved in the MS method is that the interpolation is based on a grid of ab-initio points focused on the dynamical important regions. Therefore, this method "optimized" the requirement of ab-initio calculations. Another advantage is its potentiality to be extended to polyatomic molecules. In this work, the Modified Shepard (MS) interpolation method is applied to H2/Pd(111) to investigate its performance for a system for which dissociative adsorption takes place through a direct as well as an indirect (i.e. dynamic trapping) mechanism. Dissociation, rotational excitation and diffraction order probabilities obtained from classical trajectory calculations with the MS-PES are in very good agreement with results computed with a previous and accurate PES [4]. Thus, this study confirms the MS method as a promising tool to tackle low energy adsorption dynamics of polyatomic molecules, usually dominated by trapping. References [1] J. Ischtwan and M. Collins, J. Chem. Phys. 100 (1994) 8080 [2] M.A. Collins, Theor. Chem. Acc. 108 (2002) 313 [3] C. Crespos, M.A. Collins, E. Pijper and G. J. Kroes, J. Chem. Phys. 120 (2004) 2392 [4] H. F. Busnengo, C. Crespos, W. Dong and A. Salin, J. Chem. Phys. 116, 9005 (2002).