Hydrogen motion on a Cu surface: A model study of the rate of single and double site-to-site jumps and the role of the motion perpendicular to the surface

We use the Miller, Schwartz, and Tromp flux–flux correlation function formula to calculate the rate coefficient for site-to-site hopping by an adsorbed hydrogen atom on Cu(100). We examine several one- and two-dimensional models with a rigid surface. We reach several qualitative conclusions which are relevant to real systems: the motion perpendicular to the surface plays a very important role in determining the site-to-site hopping rate; there is substantial barrier recrossing which makes transition state theory inaccurate; at moderate temperatures multiple jumps become important.