Theory of Hydrogen on Metal Surfaces

Abstract

The embedded atom method [6.1, 2] is used to study the classical behavior of hydrogen at all coverages on the Ni(110) and Pd(lll) surfaces. For both surfaces, the hydrogen adsorption site is predicted to be the threefold site in agreement with the experimental observations. For Ni(110) the lowest energy ordered structure at ⊝=1 is computed to be the (2 × 1). Molecular dynamics simulations of this system show a critical temperature for the order-disorder transition to be between 150 K and 200 K. For the Pd(lll) surface, two structures

$$\left( {\sqrt 3 \times \sqrt 3 } \right)$$

and

$$\left( {\sqrt 12 \times \sqrt 12 } \right)$$

R30º are predicted to be very close in energy. Quantum corrections are expected to make the

$$\left( {\sqrt 3 \times \sqrt 3 } \right)$$

R30º lower in energy. Monte Carlo simulations at θ=1/3 and 2/3 indicate that the order-disorder transition occurs near 125 K at both of these coverages with lower critical temperatures away from these ideal coverages. These predictions agree well with experimental observations.