Adsorbate cluster expansion for an arbitrary number of inequivalent sites

The detailed knowledge of a system's ground state is the most important prerequisite to understand its physical properties. We have extended the cluster-expansion formalism to apply it to adsorbate systems with an in-principle arbitrary number of adsorbate sites. The formalism will be applied to a system where a number of different adsorbate sites are occupied already at T=0 K, H on the Ir(100)-(5×1)-H surface. It will be shown that our predictions are in quantitative agreement with the experiment.