The second Chapter of this thesis is mainly devoted to a re\-iew of the dynamical charge concept in solid state physics. In Chapter 3 we briefly discuss the theoretical tools used in this work, namely density functional theory and density functional perturbation theory. Chapter 4 provides an extension of the dynamical charge neutrality condition to the case of a crystalline surface, which gives rise to a novel formulation for the acoustic sum rule. Our results concerning the Schottky barrier height calculation for the Al/GaAs(OOl) junction are presented in Chapter .5, while Chapter 6 is dernted to a detailed description of the morphology induced variations of the Schottky barrier, and a rationale for the results is given in terms of the dynamical charges. In Chapter 7 we present a study of the electronic states at the interface, of their decay length within the semiconductor, of their robustness under metal deposition and semiconductor ionicity. Finally, the last Chapter is devoted to our conclusions.