Introduction

Traditionally, pair-potentials have allowed to study atomistically the thermodynamics of alloys, surfaces and interfaces. With the advent of N-body (1) potentials it is nowadays possible to extend the above studies to complex systems and include the effect the of atomic relaxations in a consistent and unified way.

We use the constant pressure, temperature and chemical potential difference Monte-Carlo method and an N-body potential with parameters determined from the T = 0 K bulk properties (lattice constant, cohesive energy and the elastic properties) of Cu, Au and Cu₃Au, to investigate systematically bulk properties and antiphase boundaries of Cu₃Au and CuAu, as well as twisted and tilted boundaries and the [001] surface of Cu$_{\rm 3}$Au for temperatures below and above the bulk order-disorder transition temperature. Our interest is especially focused on the stoichiometry at the interfaces, examining if one of the constituents segregates to the interface or the surface and how the atoms are arranged under the influence of the strains which exist at the interfaces.