On the performance of eleven DFT functionals in the description of the vibrational properties of aluminosilicates

The performance of eleven DFT functionals in describing the equilibrium structure and the vibrational spectra at the Gamma point of pyrope (Mg3Al2Si3O12), forsterite (alpha-Mg2SiO4), alpha-quartz (alpha-SiO2) and corundum (alpha-Al2O3) is discussed. The four systems, for which accurate experimental data are available, are here used as a representative sample of the large aluminosilicates family. Calculations were performed with the periodic ab initio CRYSTAL code by using all-electron Gaussian-type basis sets. All the functionals here considered provide reasonable structural predictions, the hybrid PBE0 giving the least deviation from the experimental unit cell volumes (from -0.3% to +0.6%). At the other extreme, SVWN and SPWLSD (similar or equal to -3%) And PBE and PW91 (similar or equal to +3%) provide the largest volume under- and over-estimation, respectively. Vibrational frequencies are more accurate when computed with hybrid functionals, with the best performance provided by B3LYP and WC1LYP (mean absolute differences with respect to experiments evaluated on a set of 134 vibrational frequencies, vertical bar(Delta) over bar vertical bar similar or equal to 5.5 cm(-1)). The three recently proposed GGA functionals, PBEsol, SOGGA-PBE and WC-PBE, provide a good description of the vibrational spectra, of the same quality as the one provided by PBE0 and B1WC (vertical bar(Delta) over bar vertical bar(t) similar or equal to 10 cm(-1)), whereas poorer results are obtained with PBE (vertical bar(Delta) over bar vertical bar(t) similar or equal to 17 cm(-1)).