Dynamic and Static Defects
Hitherto we have been dealing with the dynamics of perfect alkali halide crystals. We have therefore been able to exploit to the full the lattice periodicity in order to reduce the direct-space force- constant matrix for the whole crystal to a set of independent 6x6 matrices whose eigenvalues give the squares of the normal-mode frequencies. If there is a single impurity present in the lattice, the periodicity is destroyed. It is then necessary, in principle, to return to the full set of direct-space equations of motion and attempt to solve these. In general, this is an intractable problem. However, certain theoretical techniques have been developed in order to circumvent this difficulty. These techniques are based on the fact that a complete solution is not necessary in order to compute experimentally measurable quantities.
KeywordsDipole Moment Light Curf Static Defect Relaxation Energy Weighted Density
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