At present, there is an increasing interest in the prediction of properties of classical and new materials such as substitutional alloys, their surfaces, and metallic or semiconductor multilayers. A detailed understanding based on a thus of the utmost importance for fu microscopic, parameter-free approach is ture developments in solid state physics and materials science. The interrela tion between electronic and structural properties at surfaces plays a key role for a microscopic understanding of phenomena as diverse as catalysis, corrosion, chemisorption and crystal growth. Remarkable progress has been made in the past 10-15 years in the understand ing of behavior of ideal crystals and their surfaces by relating their properties to the underlying electronic structure as determined from the first principles. Similar studies of complex systems like imperfect surfaces, interfaces, and mul tilayered structures seem to be accessible by now. Conventional band-structure methods, however, are of limited use because they require an excessive number of atoms per elementary cell, and are not able to account fully for e.g. substitu tional disorder and the true semiinfinite geometry of surfaces. Such problems can be solved more appropriately by Green function techniques and multiple scattering formalism.

Engineering materials with desirable physical and technological properties requires understanding and predictive capability of materials behavior under varying external conditions, such as temperature and pressure. This immediately brings one face to face with the fundamental difficulty of establishing a connection between materials behavior at a microscopic level, where understanding is to be sought, and macroscopic behavior which needs to be predicted. Bridging the corresponding gap in length scales that separates the ends of this spectrum has been a goal intensely pursued by theoretical physicists, experimentalists, and metallurgists alike. Traditionally, the search for methods to bridge the length scale gap and to gain the needed predictive capability of materials properties has been conducted largely on a trial and error basis, guided by the skill of the metallurgist, large volumes of experimental data, and often ad hoc semi phenomenological models. This situation has persisted almost to this day, and it is only recently that significant changes have begun to take place. These changes have been brought about by a number of developments, some of long standing, others of more recent vintage.

At present, there is an increasing interest in the prediction of properties of classical and new materials such as substitutional alloys, their surfaces, and metallic or semiconductor multilayers. A detailed understanding based on a thus of the utmost importance for fu microscopic, parameter-free approach is ture developments in solid state physics and materials science. The interrela tion between electronic and structural properties at surfaces plays a key role for a microscopic understanding of phenomena as diverse as catalysis, corrosion, chemisorption and crystal growth. Remarkable progress has been made in the past 10-15 years in the understand ing of behavior of ideal crystals and their surfaces by relating their properties to the underlying electronic structure as determined from the first principles. Similar studies of complex systems like imperfect surfaces, interfaces, and mul tilayered structures seem to be accessible by now. Conventional band-structure methods, however, are of limited use because they require an excessive number of atoms per elementary cell, and are not able to account fully for e.g. substitu tional disorder and the true semiinfinite geometry of surfaces. Such problems can be solved more appropriately by Green function techniques and multiple scattering formalism."