STRUCTURAL RELAXATIONS, PHONONS, AND ISING-MODELS

Lattice models such as Ising or Potts models are very often successful ly applied to order disorder phenomena in solids (e.g., for alloys) or on surfaces (e.g., for physisorption). In this contribution it is sho wn how to derive such models from a microscopic Hamiltonian in the fra mework of classical statistical mechanics. Both structural relaxations and thermal fluctuations can be incorporated within the (temperature- dependent) parameters of the lattice model.