In the present study, we performed first-principles modeling of calculation on electricity behavior of ferroelectric strontium bismuth tantalate (SBT). Different cluster models were chosen for the discussion of the influence of atomic coordination on the atomic valence configuration, atomic charge, and bond order etc. in the DV-Xalpha calculations. This allowed us to understand size effects of cluster on the electronic structure of SBT. The results of first-principles calculations of the electronic structure in SrBi2Ta2O9 (SBT) were reported. The electronic density distribution indicates density of states induced local levels within the gap, and finds significant hybridization between metal d states and the O-2p-Ta-5d and Ta-6s state. The charge of Sr is transferred to the oxygen atom, the bonding between them was nearly ionic bonding. The calculated electronic structure of SBT indicates that the absence of an energy gap in the vicinity of the fermi level stems from lowering of the Sr orbital energies due to its lower electro-negativity relative to Ta and Bi ions, and significant hybridization between Ta, Bi and 0 ions. The calculated total densities of states were in agreement with the reported X-ray photoemission spectroscopy data. (C) 2003 Elsevier Ltd. All rights reserved.