68 eV, consistent with previous results. Our computed adsorption energy grid in Fig. shows that the per atom adsorption energies of all configurations exhibit only a weak dependence on surface coverage. The lowest adsorption energy in each of the low-coverage, high-coverage, fcc-occupied, and hcpoccupied quadrants are all quite similar relative to bulk absorption, within a range of 0.085 eV/H. The lowest adsorption energy is observed in the fcc-occupied quadrant (see Fig. ), with a value of ∆∆e (111) f cc7 = 0.19 eV/H. Random sampling in Fig. shows that ∆∆e energies are relatively flat with surface coverage. Adsorption energies on (111) are minimized at moderate coverage in the range 0.3 < θ < 0.5 rather than at low coverage as on (100). Similar to the (100) surface, the energies of randomized structures are also bounded by the convex hull of structures examined for Fig. . Due to the similarity in energies for hcp and fcc sites, the (111) surface is likely to fill randomly with increasing P H2 .