DFT calculation of vibrational frequencies of clusters in GaAs and the Raman spectra

We have calculated the vibrational frequencies of clusters of Ga and As atoms from the first principles using the density-functional theory (DFT) method and the local-density approximation (LDA). We find that the calculated value of 286.2 cm(-1) for a linear cluster of Ga2As2 is very near the experimental value of 292 +/- 4 cm(-1). The calculated value of 289.4 cm(-1) for Ga2As6 (dumb bell) cluster is indeed very near the experimental value. There are strong phonon correlations so that the cluster frequency is within the dispersion relation of the crystal LO value. There is a weak line in the experimental Raman spectrum at 268 cm(-1) which is very near the value of 267.3 cm(-1) calculated for the Ga2As (triangular) cluster. The weak lines corresponding to the linear bonds provide the strength to the amorphous samples. There are clusters of atoms in the glassy state of GaAs. (C) 2012 Elsevier B.V. All rights reserved.