Intensities of the vibrational spectra of siliceous zeolites by molecular dynamics calculations. I. Infrared spectra

Two models based on electrooptical parameters and one model using the fixed -charge approximation are tested for the calculation of the infrared intens ities of the vibrational modes deduced from molecular dynamics calculations of four siliceous zeolites: sodalite, faujasite, zeolite A, and silicalite . The best results are obtained from the electrooptical model containing tw o parameters: the equilibrium bond dipole moment of the SiO bond and the de rivative of this dipole moment with respect to the SiO bond length. The rat io of these two parameters, 0.93 Angstrom, determined previously is a good compromise permitting a reproduction of the relative intensities throughout the whole frequency range. The bond-stretching high-frequency range greate r than 1000 cm(-1) is dominated by the second parameter. The first paramete r essentially controls the frequency range less than 700 cm(-1).