Cation polarizability from first-principles: Sn 2+

Abstract

Generalized Gradient Corrected Density Functional Theory calculations have been performed on SnO in the gas phase. The total charge density of the molecular system has been partitioned between Sn and O using a Wannier localization transformation of the Kohn Sham eigenvectors, and the single-ion dipole moment of Sn 2+ at the optimized bond-distance has been estimated in terms of the position of the resulting Wannier function centers. This analysis has been extended over a wide range of ionic separations in order to monitor the dependence of the Sn 2+ dipole on both Coulombic and short-range interactions with O 2−. The mechanism responsible for Sn 2+ polarization proves to be easily explained in terms of the non-bonding orbital center distance from the nucleus, without any major contributions deriving from mixing with orbitals centered on O. The Sn 2+ polarizability in the molecular system at the optimized bond distance (15.23 a.u.) is intermediate between the value for the free-ion (14.50 a.u.) and the estimate for crystalline SnO in the rocksalt structure (15.83 a.u.). The bond-length dependent polarizability at large ionic separations shows excellent agreement with the available Hartree Fock free-ion value.