THE LATTICE-CONSTANT OF ADSORBED METAL MONOLAYERS WITH INCOMMENSURATESTRUCTURE

A simple model for an incommensurate dense metal layer adsorbed on a m etal substrate is presented, in which both metals are represented as j ellium with pseudopotentials. It is first shown that a single lattice plane detached from the bulk metal tends to contract, because the elec trostatic attraction from the neighboring planes is missing. When the monolayer is brought in contact with the adsorbate the lattice constan t expands again, but is still shorter than for a bulk metal.