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Structure and pressure variation of the anion polarizability and dependent properties in solid magnesium oxide.

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Bibliographic Details
Title:	Structure and pressure variation of the anion polarizability and dependent properties in solid magnesium oxide.
Authors:	Pyper, N. C.
Source:	Molecular Physics. 09/01/98, Vol. 95 Issue 1, p1-15. 15p. 12 Charts, 3 Graphs.
Subjects:	Magnesium compounds, Polarizability (Electricity), Anions
Abstract:	Ab initio electronic structure computations yield the polarizability alphaA (R) of the O2 ion in the 4-coordinated B3, B1 rocksalt and 8-coordinated B2 phases of solid MgO over a wide range of closest cation-anion separations R . In all three phases and in the point lattices for the B1 and B2 structures, the anion size as measured by (r2)tot, the mean-square distance of all the anion electrons, controls alphaA (R) in exactly the same way since these values all lie on the same smooth curve when plotted against 4((r2)tot)2 /90. The Birch-Murnaghan equation of state yields the pressure for which any R is the equilibrium distance. For pressures occurring in the mantle of the earth, alphaA (R) is substantially reduced from its value under ambient conditions. For each of the three phases, the variation of the O2 polarizability over the entire range of distances of any possible practical importance can be represented by a single exponential increase with increasing R. The R dependence of alphaA (R) modifies that of the interionic dispersive attractions and high frequency dielectric constant governed by the Clausius-Mossotti relation. The analytical expression for the R dependence of alphaA (R) is used to derive the derivative with respect to distance of both these properties, and hence the pressure dependnece of the dielectric constant and refractive index at zero pressure. The numerical values presented for these latter derivatives are more than than ten times smaller than would be predicted if alphaA (R) were taken to be constant. [ABSTRACT FROM AUTHOR]
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Database:	Engineering Source

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Abstract:	Ab initio electronic structure computations yield the polarizability alphaA (R) of the O2 ion in the 4-coordinated B3, B1 rocksalt and 8-coordinated B2 phases of solid MgO over a wide range of closest cation-anion separations R . In all three phases and in the point lattices for the B1 and B2 structures, the anion size as measured by (r2)tot, the mean-square distance of all the anion electrons, controls alphaA (R) in exactly the same way since these values all lie on the same smooth curve when plotted against 4((r2)tot)2 /90. The Birch-Murnaghan equation of state yields the pressure for which any R is the equilibrium distance. For pressures occurring in the mantle of the earth, alphaA (R) is substantially reduced from its value under ambient conditions. For each of the three phases, the variation of the O2 polarizability over the entire range of distances of any possible practical importance can be represented by a single exponential increase with increasing R. The R dependence of alphaA (R) modifies that of the interionic dispersive attractions and high frequency dielectric constant governed by the Clausius-Mossotti relation. The analytical expression for the R dependence of alphaA (R) is used to derive the derivative with respect to distance of both these properties, and hence the pressure dependnece of the dielectric constant and refractive index at zero pressure. The numerical values presented for these latter derivatives are more than than ten times smaller than would be predicted if alphaA (R) were taken to be constant. [ABSTRACT FROM AUTHOR]
ISSN:	00268976
DOI:	10.1080/00268979809483128