There is no a priori reason to choose a particular function to fit the spectrum. Empirically, the visible Raman spectra of amorphous carbons show one or two prominent features (the G and D peaks) and some minor modulations … The simplest fit consists of two Lorentzians or two Gaussians. A Lorentzian fit is often used for crystals, arising from finite lifetime broadening, and it is normally used for disordered graphite. A Gaussian line shape is expected for a random distribution of phonon lifetimes in disordered materials. A simple two symmetric-line fit is not always suitable, and one can find a multipeak fit" .