Homogeneous polarisation field

At present, the /-values of the noble gases are not known adequately enough to base such a calculation on them. But we can provisionally give an estimate for (7) with the help of its relation to the energy of a polarisable molecule in a homogeneous electrostatic field T = Tz-, of which the force lines lie in the Z-direction. This reads, on averaging all orientations. 

For an electron in a high AC field, a solution of the Schrodinger equation exists which is analytic, and therefore plays a fundamental role, rather like the hydrogenic solution in relation to atomic physics. If we consider a plane polarised, homogeneous and infinite classical wave1... 

As one moves towards the realm of condensed matter physics, the hope of a wavefunction-based theory involving an exact treatment of spin-jK>larisation and exchange fades. Most modem work in this field is carried out within the density functional theory (DFT) introduced by Hohenbei, Kohn and Sham [1,2], in which the electron density tak i on the role of the primary variable. This allows scope for any number of s roximate treatments of electronic exchange and correlation, so that calculations for even the largest s> tems become tractable. Insofar as spin-polarisation is included, it is tinted in a parametric maimer, making use of exact results obtained for the homogeneous electron gas. 

We consider further the case in which the system is subject to the action of an external homogeneous field and spatial quantisation exists (which is approximately true for weak fields). The alterations of m and the polarisation of the light are then subject to the rules derived above. It is easy to see that the transition possibilities Aj = —1, 0, +1, which are valid for a free system, remain true for j. 

When an electric field is applied to a material, an induced dipole moment connected to the polarisability appears. This dipole moment comes from a non-homogeneous repartition of the electrical charges in the material. That repartition corresponds to several types of polarisation [108]. 

A polarisable apolar molecule can be represented by a dielectric sphere of radius a and relative permittivity 8, bearing no diarge distribution vdiidi can produce singularities for r g a. An ion or polar molecule situated in the vidnity of this sphere give rise to an induced dipole moment in and hence to an electrostatic field around the dielectric sphere. The solvent around the apolar molecule is considered as a homogeneous medium of relative permittivity s. 

Total through-bond correlation technique using adiabatic pulses and fast MAS has been suggested by Hardy et al It has been shown that above a certain threshold, the polarisation transfer achieved with these sequences is largely insensitive to the amplitude and homogeneity of the radiofrequency field employed. An experimental transfer efficiency of up to 76 /o was achieved in a two-spin system. Applications to resonance assignments in the dipeptide L-Val-... 

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