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Vibration properties of Zn(1-x)Be(x)Se, a mixed II-VI semiconductorharacterized by a high contrast in elastic properties of its pure constituents,ZnSe and BeSe, are simulated by first-principles calculations of electronicstructure, lattice relaxation and frozen phonons. The calculations within thelocal density approximation has been done with the Siesta method, usingnorm-conserving pseudopotentials and localized basis functions; the benchmarkcalculations for pure endsystems were moreover done also by all-electron WIEN2kcode. An immediate motivation for the study was to analyze, at the microscopiclevel, the appearance of anomalous phonon modes early detected in Raman spectrain the intermediate region (20 to 80%) of ZnBe concentration. This was earlydiscussed on the basis of a percolation phenomenon, i.e., the result of theformation of wall-to-wall --Be--Se-- chains throughout the crystal. Thepresence of such chains was explicitly allowed in our simulation and indeedbrought about a softening and splitting off of particular modes, in accordancewith experimental observation, due to a relative elongation of Be--Se bondsalong the chain as compared to those involving isolated Be atoms. The variationof force constants with interatomic distances shows common trends in relativeindependence on the short-range order.Comment: 11 pages, 10 figures, to be published in Phys. Rev.

Lattice dynamics of the mixed semiconductors (Be,Zn)Se from first-principles calculations