The prospect of lattice structure and ferroelectricity of SnTiO3 have been studied by first-principles calculations within local density approximation. The results showed that the SnTiO3 has the minimum total energy within almost tetragonal perovskite structure of a=b=3.80 Å, c=4.09 Å. The calculated electronic structure of SnTiO3 resembles that of PbTiO3 because the Ti 3d states, Sn 5s and 5p states hybridize with the O 2p orbitals. The moment of spontaneous polarization of SnTiO3 was estimated as 73 μ C/cm2, which is as large as that of PbTiO3.
Recent developments in the study of high Rydberg states require the calculation of radial integrals for dipole transitions between states of large effective principal quantum numbers v, v' and non-zero quantum defect. The method of Bates and Damgaard breaks down in such cases, while that of Edmonds and Kelly makes it possible to reach v = 40, which is often inadequate.We present a technique of extrapolation based on data given by the latter method, which, by judicious choice of the variable of expansion, makes it possible to obtain radial dipole integrals for arbitrarily large v , v' in terms of four functions of the difference vv' with convenient symmetry properties. These functions have been tabulated and representative curves are shown here.
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