Influence of the exchange-correlation functional in all-electron calculations of the vibrational frequencies of corundum (α-Al2O3)

The equilibrium structural parameters, high- and low-frequency dielectric tensors, Born effective charges, and F-point vibrational frequencies of bulk Al2O3 corundum are calculated by using the periodic, ab initio program CRYSTAL, which adopts an all-electron Gaussian-type basis set. The effect of basis set and the performance of three different functionals, i.e., LDA, PW91, and B3LYP, are discussed. The mean absolute deviation from the measured frequencies is as small as 7 cm(-1) for both the LDA and B3LYP functionals, indicating that these functionals perform extremely well in this case. The mean absolute deviation increases to 18 cm(-1) when the PW91 functional is used. All three functionals reproduce the equilibrium geometry of corundum to a high level of accuracy, with LDA and B3LYP outperforming PW91 slightly. The comparison of the current all-electron calculations with previous plane-wave, pseudo-potential calculations shows an overall similar performance. The results of isotopic substitution for both Al and O are also presented.