SURFACE RELAXATION IN CRYSTALS WITH SPATIAL-DISPERSION

Static response functions are derived for crystals with surfaces in a harmonic model showing spatial dispersion. The relaxed structure is then described by analytical formulae in crystals in which local stresses arise due to the presence of surfaces and in materials subject to macroscopic uniaxial stress with the axis either perpendicular or parallel to the surfaces. Pretransitional appearance of the new phase and the creation of antiphase domain walls in the crystals with surfaces are shown to be a consequence of thermal variation of effective force constants when the materials approach their structural phase transitions.