The structure and the vibrational spectrum of akdalaite (5Al 2 O 3 ·H 2 O, also known as tohdite) have been investigated at the periodic ab-initio quantum-mechanical level by using a high quality Gaussian type basis set and the hybrid B3LYP Hamiltonian with the CRYSTAL06 code. Three space groups proposed in the literature, namely P6 3 mc and its two P31c and Cmc2 1 subgroups, have been considered, obtaining essentially the same energy (the largest total energy difference is 0.2 kJ/mol per cell) and geometry. The harmonic frequencies at the τ point have been computed. Isotopic substitution and graphical representation permit a complete classification of normal modes in terms of simple models (octahedra and tetrahedra modes, hydrogen stretching and bending). The Al-O octahedra and tetrahedra modes appear below 880 cm -1, Al-OH bending modes are located in the range 870-900 cm -1, and OH stretching modes are at 3330-3400 cm -1.

Ab initio quantum mechanical study of akdalaite (5 Al2O3 · H2O): structure and vibrational spectrum

DEMICHELIS, Raffaella;ROETTI, Carla;VALENZANO, LOREDANA;DOVESI, Roberto
2008-01-01

Abstract

The structure and the vibrational spectrum of akdalaite (5Al 2 O 3 ·H 2 O, also known as tohdite) have been investigated at the periodic ab-initio quantum-mechanical level by using a high quality Gaussian type basis set and the hybrid B3LYP Hamiltonian with the CRYSTAL06 code. Three space groups proposed in the literature, namely P6 3 mc and its two P31c and Cmc2 1 subgroups, have been considered, obtaining essentially the same energy (the largest total energy difference is 0.2 kJ/mol per cell) and geometry. The harmonic frequencies at the τ point have been computed. Isotopic substitution and graphical representation permit a complete classification of normal modes in terms of simple models (octahedra and tetrahedra modes, hydrogen stretching and bending). The Al-O octahedra and tetrahedra modes appear below 880 cm -1, Al-OH bending modes are located in the range 870-900 cm -1, and OH stretching modes are at 3330-3400 cm -1.
2008
117
012013-1
012013-8
http://stacks.iop.org/1742-6596/117/i=1/a=012013
R. Demichelis; Y. Noel; C. M. Zicovich-Wilson; C. Roetti; L. Valenzano; R. Dovesi
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/132589
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