Theoretical Calculations of Shieldings in Alkali Halide Crystals

Theoretical Calculations of Shieldings in Alkali Halide Crystals 

In view of the importance of theoretical calculations of shieldings in alkali halide crystals for our present knowledge of we will here briefly outline the models used. 

It would seem that at least two of the models, (i) and (ii), actually are two expressions of the same realization that the wave function for a halogen ion in an alkali halide crystal no longer can be accurately described by that of an isolated ion but must be modified. Whereas Yosida and Moryia write the new wave function as a linear combination of purely ionic and purely covalent basis functions, Kondo and Yamashita write the ground state wave function as a single determinant of one-electron wave functions. The latter are chosen as Lowdin s orthogonalized orbitals which take into account 

In the following we will leave out the subscript X whenever the meaning is clear from the context. 

The starting point for the Kondo and Yamashita overlap model is the equation for the nuclear shielding tensor a due to Ramsey [25], 

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SR = calculated from measured spin rotation constants in molecular beam experiments. Aik.Hal. = from theoretical calculations of shieldings in alkali halide crystals. Aik.Hal. (P) = from pressure dependence of alkali halide shifts in combination with theoretical models for shielding values. T2 = calculated from experimental value of line width at infinite dilution. 6VS.T2 = calculated from concentration dependence of chemical shifts and line widths. H2O/D2O = calculated from solvent isotope effects on chemical shifts. NaVwa" = estimated from difference in chemical shift between Na and Na . Atomic beam = calculated from magnetic moment of free atom determined in atomic beam experiments. 

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