Comparative Study of Theoretical Partial Charges of Pristine and Doped GaAs Clusters Ga 3 As 3 , Ga 7 As 7 , AlGa 2 As 3 , and Al 2 Ga 5 As 7

The stable structure of (GaAs) 3 and (GaAs) 7 has been found by the first principle calculation previously. Here we use ultra-soft pseudo potentials with plane wave methods within the framework of the density functional approach to investigate the partial charge density and bonding mechanism of the pristine and doped clusters. We found that the electronic states at the vicinity of the Fermi level come mainly from p states with very small contributions from s states. Study of the orbital charge density of the doped clusters reveals that conduction is possible through molecular orbitals other than the lowest unoccupied molecular orbital level. The pristine cluster and doped clusters have Fermi level below the midgap, that is near to the HOMO level but slight difference has been observed and there is a band shift in energy levels of the doped clusters towards the higher energy level.