AB-INITIO STUDY OF HYDROGEN ADSORPTION ON PD(100)

We report an all-electron density-functional theory study of the adsor ption of hydrogen at Pd (100). We use the local-density approximation for the exchange-correlation energy functional and the full-potential linear muffin-tin orbital method (FP-LMTO) to calculate adsorption ene rgies, stable adsorption sites, adsorption-induced surface relaxations , and the work-function changes. It is found that (as expected) for co verages theta less-than-or-equal-to 1 the surface fourfold hollow site has the largest adsorption energy. For coverages theta > 1 it is pred icted that additional hydrogen is incorporated below the surface. The work function increases with hydrogen coverage up to theta = 1 but for additional hydrogen adsorption we find that DELTAPHI remains roughly constant. The theoretical results are compared with available experime ntal data.