Hydrogen-Induced Polymorphism of the Pd(110) Surface

Using density functional theory, we investigate the adsorption of hydrogen on Pd(110). We find this system to be unique in that hydrogen modifies the surface morphology into a multitude of coexisting structures, which are precursors for its solution in the bulk metal. This behavior is manifested in the energetic near degeneracy between the (1×2) paired-row and missing-row structures, and (2×1) structures containing subsurface hydrogen. The uncommon paired-row structure, induced by an incompletely screened Coulomb repulsion between adjacent rows, opens hydrogen diffusion channels into the bulk.