General expressions for the response coefficients for calculating the polarisation effects far away from the defect (via the crystal dynamical matrix) have been derived recently [B43]. These formulas are valid for an arbitrary crystal both in the bulk and at the surface. The expressions obtained in [B43] enable one to calculate separately atomic displacements and induced dipole moments on atoms in the unit cell. This is extremely important, especially when a surface defect is considered, since in this case the dielectric tensor is difficult to define.
A general method for calculating polarisation in the infinite outside region has been proposed in [A3,B18,B19]. The method does not use the continuum approximation and is based on the perfect crystal lattice dynamic Green's function (GF).
Detailed calculations made on a number of hole (H, Vk, V2) and electronic (F, F2, F-2, F+2) centres in several alkali halides [B5,B10,B15], and [Li]0-centre in MgO [B12], confirmed the decisive role of the polarisation effects in the determination of optical and vibrational properties of the defects. Calculations of radiative tunnelling transitions between electronic and hole centres as a function of their separation have also been carried out in [B3,B15]. The importance of the repolarisation correction in the transition energy (the difference between crystal polarisation energies before and after the transition) has been demonstrated in these calculations.