Quantum states of hydrogen atom motion on the Pd(111) surface and in thesubsurface

Abstract

We investigate the quantum states of hydrogen atom motion on Pd(111) surface and in itssubsurface by calculating the wavefunctions and the eigenenergies for hydrogen atommotion within the framework of the variation method on an adiabatic potential energysurface (PES), obtained through first-principles calculations, for the hydrogen atommotion. The calculated results show that the ground-state wavefunction for the hydrogenatom motion localizes on the face-centered cubic (fcc) hollow site of the surface. The higherexcited state wavefunctions are distributed between the first and second layers, andsubsequently delocalized under the second atom layer. These suggest that an effectivediffusion path of the hydrogen atom into the subsurface area passes through the fcc hollowsite to the octahedral sites in the subsurface. Moreover, activation energies for diffusion ofH and D atoms over the saddle point of the PES between the fcc hollow siteand the first (second) octahedral site are estimated as 598 (882) meV and 646(939) meV, respectively. Furthermore, the activation energies for diffusion of H and Datoms over the saddle point of the PES between the first (second) octahedralsite and the fcc hollow site are estimated as 285 (483) meV and 323 (532) meV,respectively.