Ab Initio Calculation Of Vibrational Frequencies In As_xS_(1-x) Glass And The Raman Spectra

摘要

We have made many different models for the understanding of the structure of AsS glass. In particular, we made the models of AsS_3 (triangular), AsS_3 (pyramid), AsS_4 (3S on one side, one on the other side of As, S3-As-S), AsS4 (pyramid), AsS4 (tetrahedral), AsS_7, As2S6 (dumb bell), As_2S_3 (bipyramid), As_2S_3 (zig-zag), As_3S_2 (bipyramid), As_3S_2 (linear), As4S4 (cubic), As4S4 (ring), As4S (tetrahedral), As_4S (pyramid), As_4S_3 (linear) and As_6S_2 (dumb bell) by using the density functional theory which solves the Schrodinger equation for the given number of atoms in a cluster in the local density approximation. The models are optimized for the minimum energy which determines the structures, bond lengths and angles. For the optimized clusters, we calculated the vibrational frequencies in each case by calculating the gradients of the first principles potential. We compare the experimentally observed Raman frequencies with those calculated so that we can identify whether the cluster is present in the glass. In this way we find that AsS_4 (S_3-As-S), As_4S_4 (ring), As_2S_3 (bipyramid), As_4S_4 (cubic), As_4S_3 (linear), As_2S_3 (zig-zag), AsS_4 (Td), As_2S_6 (dumb bell), AsS_3 (triangle) and AsS3 (pyramid) structures are present in the actual glass.