MODES IN AMORPHOUS-SILICON

We discuss how the vibrational modes in an amorphous material can be c haracterized by various correlation functions. The spectrum of modes c an be expected to contain both extended and localized states separated by mobility edges. The inverse participation ratio can be used as a m easure of localization. To examine the vibrational modes in more detai l, we propose to study mod;li of Fourier transforms of powers of the e igenvector components. We have applied the analysis to vibrational mod es of amorphous silicon. The structural and potential models that we u se are based on the Wooten-Winer-Weaire bond-switching algorithm and S tillinger-Weber classical potential. The structural models are cubic s upercells, periodically repealed. Whereas models ranging in size from 216 to 4096 atoms have been studied, only the 4096-atom model results are included here. In the analysis, we employ only q vectors that are consistent with the boundary conditions used to obtain the modes. Upon averaging over q-vector direction, systematic dependences result. The structural aspects of the model are briefly considered. In particular , no unusual structural ordering has been detected in the pair distrib ution function for the 4096-atom model.