Raman spectrum of NaAlSi2O6jadeite. A quantum mechanical simulation

The Raman spectrum of NaAlSi2O6 jadeite is simulated and compared with two recent experimental data sets. In one experiment, only 17 (out of 30 symmetry allowed) peaks and a qualitative estimate of the intensities are provided. In the second case, the digitalized spectrum is available, fromwhich we have been able to extract 20 evident peaks and an estimate of the relative intensities. The present calculation is based on an ab initio quantum mechanical treatment. Using an all-electron Gaussian-type basis set, together with the hybrid B3LYP density functional, the full set of 30 activemodes and their (polycrystalline and polarized) intensities are obtained. The simulated intensities (not available in a previous study of the same system) permit the two experimental spectra to be reconciled and explain why the missing peaks were not seen. This ultimately leads to excellent agreement between experiment and theory. By artificially varying the mass of the NaC and Al3C cations in the simulations, which can be performed automatically and at essentially no computational cost, the vibrational modes to which these ions contribute are identified. We conclude that quantum mechanical simulation can be a very useful complementary tool for the interpretation of experimental Raman spectra.