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Arbitrary force-constant changes in the crystal impurity problem
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DOI：10.1103/PhysRevB.73.184103.png)
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Abstract
En 中文
To calculate the response to an external probe of an impurity in a host crystal, one needs to determine both the frequencies and the amplitudes of the perturbed crystal vibrational modes in which the defect participates. When the introduction of the defect leads to force-constant changes, the complexity of the problem often necessitates a numerical treatment. However, in a previous study we had actually obtained simple and exact analytic expressions for the positions and intensities of the perturbed modes in the case in which the host-host and the host-impurity force constants were taken to be both central and nearest neighbor. Such expressions required knowledge of only one pure crystal lattice Green's function, the one at the defect site itself. In this paper we extend our previous study to incorporate nearest-neighbor noncentral force constants as well. By analytically constructing the perturbed crystal lattice Green's function at the defect site, we find that the same simple expressions, which we had previously obtained in the nearest-neighbor central force-constant case, also hold without any modification at all in the case of isotropic force-constant changes in crystals whose host-host force constants are isotropic, and in the particular mixed case in which the fractional changes in the central and isotropic components of the force constants are equal to each other. In the most general arbitrary nearest-neighbor force-constant change case we obtain a reasonably compact exact expression for the dynamics of the perturbed modes which only involves a total of two pure crystal lattice Green's functions.
Keywords:
POINT DEFECTS
Journal
IF:
3.7
Papers:
15.4W
Citations:
41.0W
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