A recent experiment determined the magnetic moment /Mn, M, in the dilute Mn<sub>x</sub>Si<sub>1-x</sub> with x = 0.1% to be 5.0 µ<sub>B</sub>/Mn.
The existing calculated M values range from 2.37 to 3.1µ<sub>B</sub>/Mn except the case with a fixed charge state, Mn<sup>2+</sup>, which
gives 5.0µ<sub>B</sub>/Mn. We address the issue: Can a single Mn at its neutral charge state in dilute MnxSi1-x alloys have M = 5.0
µ<sub>B</sub>/Mn? After carrying out extensive calculations, the only model giving this M value involves a supercell having a total
of 513 atoms with a Mn at a substitutional site and a Si at a tetrahedral interstitial site serving as a second neighbor to the
Mn. Physically, the Mn contributes 4.0 µ<sub>B</sub> due to the weakening of the d-p hybridization between the transition metal
element and its nearest neighbor Si caused by the presence of the second neighbor Si. The additional 1.0 µ<sub>B</sub> is the
consequence of the exchange interaction through the remaining weak overlap of the wave functions between the d-state
of the Mn and the sp<sup>3</sup> state of the nearest neighbor Si atom. Evidences for the weakening of the d-p hybridization are
The electronic properties of heavily and orderly Si-doped nipi structures in GaAs are studied theoretically using the abinitio self-consistent pseudopotential method within the local density approximation. Two nipi configurations are considered. Besides investigating the nature of the impurity-related band edge states the xy-planar-averaged local ionic and self-consistent potentials are also analyzed. The screening effect of the host crystal on the doping induced potential is found to be small. The effects of the doping induced electric field and the strain due to dopings are also examined.