Raman frequency calculations of Al ( H 2 O ) 6 3 + and Al ( OH ) 4 - species in different models were carried out with density functional theory (DFT). Gas-phase model (GP), polarizable continuum model (PCM), supermolecule model (SM) and supermolecule-polarizable continuum model (SM-PCM) were considered and frequencies over the wavenumber range from 0 to 1000 cm−1 were discussed. The calculated frequencies of the two species in SM-PCM model are in fair agreement with the observed frequencies in aqueous solution and the average deviation is 6 cm−1. Based on the results of Al ( H 2 O ) 6 3 + and Al ( OH ) 4 - , the DFT method and the SM-PCM model were used to study the Al–O Raman bands for some other monomeric and dimeric aluminiums. The monomeric aluminiums Al(OH)2+, Al ( OH ) 2 + and Al ( OH ) 6 3 - as well as the dimer Al 2 O ( OH ) 6 2 - were included. As a result, we predict the main Al–O skeleton vibrations of Al ( OH ) ( H 2 O ) 5 2 + at 685 cm−1, trans- Al ( OH ) 2 ( H 2 O ) 4 + at 542 cm−1, Al ( OH ) 6 3 - at 510 cm−1 and Al 2 O ( OH ) 6 2 - at 510 and 699 cm−1 respectively in Raman spectra of aqueous solution. It can also be concluded that the calculated frequencies of Al 2 O ( OH ) 6 2 - are close to the experimental values and the existence of Al ( OH ) 6 3 - in aluminate solution cannot be ruled out.
