Phonon modes, dielectric properties, infrared reflectivity, and Raman intensity spectra of semiconducting silicide BaSi2: First principles study

In this study, we investigated the phonon modes, dielectric properties, infrared (IR) reflectivity, and Raman intensity spectrum of semiconducting silicide BaSi2 within the framework of the first principles density functional theory. The zone-center phonon mode frequencies formed two major bands in the ranges of 50-150 cm−1 and 270-500 cm−1. The modes in the frequency band 100-150 cm−1 had high Born effective dynamical charges and oscillator strengths, and they contributed significantly to the mode effective charge, static dielectric permittivity, IR activities, and reflectivity spectrum. These modes were attributable to displacements of isolated Si clusters relative to one another without internal distortions. The computed Raman activities and intensities were significant for modes in the frequency band of 270-500 cm−1. These modes were primarily associated with silicon atom vibrations in the Si clusters in BaSi2 and the internal modes of the isolated Si clusters with Td symmetry. The band gap was also computed for BaSi2 using the modified Becke-Johnson exchange potential and it was in good agreement with the previously reported experimental values. The computed Raman intensity and IR reflectivity spectrum can be used as benchmark first principles theoretical results to compare with experimental results.