Units and Magnitude of Magnetic Susceptibilities

The applied magnetic field (induction) varies typically from 1-10 Tesla in NMR experiments. Sustained B-fields of 50 Tesla (1 T = 1 Wbm = 10 Gauss) are possible with special magnets At 32 Tesla the energy density (in SI units) is go — vacuum permeability=47r x 10 N A ) 

The diamagnetic contribution x is easy to calculate since it is only a ground state average. Experience shows that it is rather insensitive to electron correlation. The calculated values of (r ) are given in Table 8.2 at the equilibrium geometry for a number of small molecules.  

The paramagnetic contribution is more demanding to calculate and is a bit more sensitive to electron correlation, although not a great deal. For instance, for ammonia, the RPA (effectively uncorrelated) value is 38.45 ppm a.u., while the Second Order Polarization Propagator Approximation (correlated) yields 38.15 ppm a.u. 

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