Formation of water at a Pt(111) surface: A study using the reactive force field (ReaxFF)
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Formation of water at a Pt(111) surface: A study using reactive force fields (ReaxFF) Markus J. Buehler1, Adri C.T. van Duin2, Timo Jacob3, Yunhee Jang2, Boris Berinov2, William A. Goddard III2 1
Massachusetts Institute of Technology, Cambridge, MA 02139, USA Materials and Process Simulation Center, California Institute of Technology, Pasadena, CA, 91125, CA 3 Fritz Haber Institute of the Max Planck Society, D-14195 Berlin-Dahlem, Germany 2
ABSTRACT In this paper, we report preliminary studies of formation of water from molecular oxygen and hydrogen. Using a series of atomistic simulations carried at finite temperature, we describe the dynamics of water formation at a Pt catalyst using a new reactive ReaxFF potential. By performing a series of studies, we obtain statistically meaningful trajectories to extract rate constants of water formation. This allows an estimate for the activation energy during water formation, which is found to be in reasonable agreement with the activation barrier calculated by restraint driven molecular dynamics simulation of water formation at the Pt surface. INTRODUCTION Water is one of the most important substances on earth, as it plays a very important role in many biological systems. However, the chemical complexities of modelling the properties of water in particular during formation of water have so far not been accessible to molecular dynamics simulations at large time and length scales necessary to describe the dynamics of realistic systems. This is because so far, atomistic modeling of chemical reactions has been limited to a few hundred atoms and very short time scales, since only DFT methods could be used to describe the correct quantum mechanical effects. Such techniques have been used to describe the processes associated with water formation and reactions at metal surfaces (see, for instance [1, 2]).
Pt H2, O2 Pt Figure 1: Schematic view of the simulation condition (a) and snapshot at the beginning of a dynamical calculation (b). A mixture of H2 and O2 molecules in stochiometric ratio embedded in a finite volume serves as a starting point.
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Figure 2: Part of the QM based training set used to develop the reactive force field for the O/H-Pt system. The force field is still under development, and for the simulations reported in this paper we have used a preliminary version of this force field (QM data by Jacab and Goddard [3]). The plot shows the relative energy as a function of the reaction coordinate as one water molecule is formed at a Pt surface.
From numerous experimental studies, it is well-known that Pt plays an important role as catalyst in the process of water formation based on molecular oxygen and hydrogen. However, to our knowledge, no direct atomistic simulation has been performed to show the effect of catalysts at finite temperature. To fill this gap, we have carried out finite temperature atomistic studies of water formation at Pt surfaces using a new first principles based reactive force field (ReaxFF) capable of describing the c
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