Abstract
A method for an ab-initio calculation of transverse dynamical effective charges Z* in partially covalent semiconductors within the framework of pseudopotential theory is presented. It is based on previously established expressions for Z* in terms of the inverse microscopic dielectric function of the crystal but circumvents the direct inversion of the latter. In contrast to earlier calculations the results are definitely boundary insensitive. Moreover, the acoustic sum rule expressing charge neutrality is inherently guaranteed. Within the local empirical pseudopotential method a simple analytical model calculation, which is compared with the bond orbital model, as well as a full numerical computation is performed. For III-V compounds the resulting Z* underestimate the experimental effective charges by approximately 30% while good agreement for II-VI materials is obtained. Reasons for these findings are discussed and the effects of several refinements are estimated.
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