The Raman spectrum of grossular garnet: a quantum mechanical simulation of wavenumbers and intensities

Abstract

Raman spectroscopy is a standard and powerful investigation technique for minerals, and garnet is one of the most observed and visible minerals, undoubtfully important both as a witness of our planet’s evolution and as a main component in many high-tech applications. This paper presents the Raman spectrum of grossular, the calcium–aluminium end-member of garnets (Ca3Al2Si3O12), as computed by using an ab initio quantum-mechanical approach, an all-electron Gaussian-type basis set and the hybrid B3LYP functional. The wavenumbers of the 25 Raman active modes are in excellent agreement with the available experimental measurements, with the mean absolute difference being between 5 and 8 cm1. The apparent disagreement between a few experimental vs calculated data can be easily justified through the analysis of the corresponding calculated peak intensities, which is very low in all of these cases. The intensities of the Raman active modes of grossular were calculated here for the first time, thanks to a recent implementation by some of the present authors that allow for accurate predictions of the Raman spectra of minerals. To the authors’ knowledge, there are no tabulated data sets for Raman intensities of grossular, although qualitative information can be extracted from the published spectra. This study can then be considered as an accurate reference data set for grossular, other than a clear evidence that quantum-mechanical simulation is an actual tool to predict spectroscopic properties of minerals.