Model calculations of substitutional transition-metal impurities in III-V semiconductors have been performed with the purpose of investigating how the defect energy levels vary as the host composition is changed. The calculations are based on the theory of Haldane and Anderson and include electron-electron interactions in a self-consistent manner. The band structure has been described in terms of an sp second-nearest-neighbor tight-binding approximation. We find that the transitionmetal acceptor energy levels have fixed positions relative to the average vacancy level or the vacuum level independent of the chemical composition of the host material. This stability is a consequence of self-consistent competition between the strongly localized Coulomb interaction at the impurity site and the hybridization with the nearest neighbors.

Multiple scattering method is used to obtain wave functions and energy levels of the 17-ntom cluster MnB,A,,. The influence of all other atoms of the crystal is assumed to produce an additional constant potential only. At the Mn site, the correction to the potential is introduced to give most probable values of the cubic field splitting parameter A . For these values of A , the g-shift and superhyperfine structure tensor are calculated and compared with experimental data.Die Methode der Vielfachstreuung wird benutzt, um Wellenfunktionen und Energieniveaus des 17-atomigen Clusters MnB,A,, zu erhalten. Der EinfluB aller anderen Atome des Kristalls wird nur als zusatzliches konstantes Potential angenommen. An den Mn-Platzen wird eine Korrektur zum Potential eingefuhrt, die die wahrscheinlichsten Werte des kubischen Anfspaltungsparameters d ergibt. Fur diesen Wert von A werden die g-Verschiebung und der Tensor der Superhyperfeinstruktur berechnet und mit experimentellen Werten verglichen.

and Sektion Physik d e r Kar,l-Marx-Universitat , Leipzig (b) 2+ Ligand Hyperfine Structure of Mn in ZnSe as Calculated by EHT-SCCC , Scattered-Wave, and LCAO Methods BY S.W. BIERNACKI (a), M. HAMERA (a), and S. WARTEWIG (b)One of the characteristics of iron group ions resulting from their incorporation a s impurities into crystals is the delocalization of the d electrons into neighbouring atoms, and it i s known /1/ that hyperfine interactions with nuclei neighbouring the impurity a r e mostly due to this delocalization. Here we report the numerical estimations of the ligand hyperfine structure parameters of ZnSe:Mn 2+ based on three models, namely: EHT-SCCC (Extended Hiickel Theory-Self-consistent Charge and Configuration), scattered-wave, and LCAO methods.