Modeling of the Dissociative Adsorption of Methane on Ir(111) from First Principles

MOIRAGHI, R; A. LOZANO; DONG, W.; BUSNENGO, H.F.

Workshop; 16th workshop Dynamical Phenomena at Surfaces (WDPS); 2014

The dissociative adsorption of methane on metal surfaces is a model system for the study of gas-surface reactions involving polyatomic molecules. The recent developments of the experimental techniques allows today, to perform high-precision measurements of the reactive properties of these systems under a variety of well-controlled conditions.[1] Reaction specific Tersoff-like reactive force fields (RFF) have been recently employed with success in the modeling of methane dissociation on Ni(111) and Pt(111). Through classical trajectory calculations its use for Pt(111) allowed to explain the high C-H bond selectivity experimentally achieved for all the partially deuterated isotopologues of methane by exciting judiciously chosen particular vibrational modes.[2] In this work, we develop a Tersoff-like RFF specific to describe methane dissociation on Ir(111). First, we have performed an exhaustive exploration of the potential energy surface (PES) through Density Functional Theory (DFT). The exploration consisted in the search for transition states (TS) on different surface sites and molecular orientations on Ir(111) and many other configurations involving molecular and surface distortions, and other extracted from Ab-initio molecular dynamics (AIMD) calculations. For the rigid surface, we have found a lowest energy TS of 0.84 eV, which decreases to 0.66 eV when surface relaxation is allowed in line with the significant surface temperature effects observed experimentally. Then, we have used most of the DFT results mentioned above to build a configuration database that was employed to optimize the parameters defining the RFF by using a non-linear least-square method. The developed RFF reproduces well all the DFT energies included in the input database, errors being e.g., not larger than ~50 meV for the DFT TSs with and without allowing surface relaxation. Moreover, the TSs geometries predicted by the RFF are very close to those predicted by DFT which is certainly necessary for realistic MD simulations in progress in our group. [