First-principles modeling of the infrared spectrum of kaolinite

The theoretical infrared spectrum of kaolinite [Al2Si2O5(OH)(4), triclinic] was computed using ab initio quantum mechanical calculations. Calculations were performed using the Density Functional Theory and the generalized gra dient approximation. The low-frequency dielectric tensor of kaolinite was d etermined as a function of the light frequency using linear response theory . The IR spectrum was then calculated using a model that takes into account the shape and size of kaolinite particles. A remarkable agreement was obta ined between theory and experiment, especially on the position of the stret ching bands of OH groups. This agreement provides a firm basis for the inte rpretation of the IR spectrum of kaolinite in terms of structural parameter s.