The electronic structures of commensurate Ru(0001)-(3 × 3)-4Kr and Ru(0001)-(5 × 5)-Kr using density functional theory

We have calculated the minimum energies for each of three positionings of the adatom unit cells for Ru(0001)-(3 × 3)-4Kr (high Kr coverage) and for Ru(0001)-(5 × 5)-Kr (low Kr coverage). The differences between the results for the low and high-coverage cases may clarify puzzles posed by the experimental results of Narloch and Menzel. The low-coverage solution converges to a structure having Kr in the top site at a height of 3.09 Å above the substrate with the adsorption energy 185 meV. In the high-coverage case, adatom unit cells with a corner Kr at top, fcc hollow, and hcp hollow locations are found to have nearly the same adsorption energy of 175 meV. The height of the corner atom above the substrate is found to be 3.35, 3.54, and 3.50 Å for the top, fcc hollow and hcp hollow sites, respectively. These results are explained by demonstrating that there is an enhancement of the substrate electronic density of states at krypton orbital energies in the low-coverage case.