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The local structures and the electron paramagnetic resonance (EPR) g factors g(parallel to) and g(perpendicular to) for the substitutional V(4+) and Cr(4+) at the Ge(4+) sites in Bi(4)Ge(3)O(12) are theoretically investigated from the perturbation formulas of the g factors for 3d(1) and 3d(2) ions under tetragonally elongated tetrahedra. In the calculations, the ligand orbital and spin-orbit coupling contributions are taken into account from the cluster approach in view of the covalency of the systems. The local impurity-ligand bond angles beta related to the C(4) axis in the V(4+) and Cr(4+) centers are found to be about 5 degrees and 6 degrees, respectively, lower than the host angle beta(H) in the pure crystal. So the ligand tetrahedra transform from original compression at the host Ge(4+) site into elongation in the impurity centers due to the size mismatching substitution of the smaller Ge(4+) by the larger impurities. Meanwhile, the Jahn-Teller effect also brings forward some contribution to the local structure of the V(4+) center. The calculated g factors are in good agreement with the experimental data. The local structures of both centers are discussed. (C) 2010 Elsevier B.V. All rights reserved.