Shielding diamagnetism

Table 1. Variation of fractional shielding diamagnetism as a function of composition x during different stages of preparation. The relaxation stage values were reproducible to 5% (determined for two or more samples at several compositions).

The atomic hypothesis was investigated in an exhaustive manner by Maksic. He tested the the Independent Atoms in Molecule (lAM) and the Modified Atoms in Molecule (MAM) models for some simple physical observables as diamagnetic shielding, diamagnetic susceptibility and ESCA shifts. It seems that these parameters can be considered as pretty sensitive probes of the wave function quality. In this context it might be surprising that for certain properties even the lAM model is able to give reliable estimates. Nevertheless, in most cases one should take into account that the atoms are considerably modified by their molecular environment [47-50]. 

The two primary causes of shielding by electrons are diamagnetism and temperature-independent paramagnetism (TIP). Diamagnetism arises from the slight unpairing of electron orbits under the influence of the magnetic field. This always occurs so as to oppose the field and was first analysed by Lamb [7]. A simplified version of his fomuila. 

Diamagnetic shielding factor, spherical water 1 + crCHjO) 1.000 025 64(7) ... 

Electromagnetic and Radiofrequency Shielding. Because bismuth is highly diamagnetic, its ahoys are quite useful in appHcations where electronic equipment must be protected from outside interference or where equipment can cause outside interference. 

The shielding tensor, and its diamagnetic and paramagnetic components, are not necessarily symmetric in the Cartesian indices [25-29], and the shielding tensor can in general be decomposed into a symmetric and an antisymmetric component, i.e. 

A common origin paramagnetic contribution can subsequently be obtained as the difference between the LORG total shielding tensor and the diamagnetic contribution from eq.(29), i.e. 

As indicated, the possibility of orbital decomposition is retained in the diamagnetic and paramagnetic terms in eqs.(29,30). The value for the paramagnetic shielding contribution extracted via eq.(30) does not, of course, correspond to a well-defined basis set, but is at the same level of numerical quality as the LORG calculation used for the total shielding. 

Lower left panel diamagnetic core- -sigma shielding. 1 A 80 ppm. 

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