Unraveling the significance of Raman modes, Gruneisen parameters and phonon lifetimes in the hexagonal allotropes of Silicon and Germanium compounds

Advancement in quantum information and quantum technologies has ushered in a new era of technological revolution in large scale atomistic simulation and efficient system on a chip device fabrication. This has led to innovative ways of harnessing rigorous search algorithms for functional quantum materials and steered scientists to dig deeper into the world of quantum phenomenon and applications. In this work, we delineate the advanced electronic structure and vibrational properties utilizing the popular meta-GGA functionals, spectral signatures of the Raman active phonon modes, explored their average mean free paths, and whether they conserve helicity, by leveraging first principles density functional theory and density functional perturbation theory. A systematic analysis of the role of phonon lifetimes, consequences of phonon-phonon and three phonon scattering rates and phonon linewidths have been presented. Further, a study of the the frequency and temperature dependent Gruneisen parameter has been employed in conjecture with the temperature dependent thermal expansion and thermal conductivity to portray the effect of anharmonicity in the phonon spectra of these two materials. Finally, we provide strategies for tuning the properties of these materials in an effort to improve their efficacy for advanced thermoelectric, photovoltaic and optoelectronic device applications.