1ST PRINCIPLES MOLECULAR-DYNAMICS CALCULATION OF THE STRUCTURE AND ACIDITY OF A BULK ZEOLITE

Local density functional theory within the framework of the Car-Parrin ello method has been used to study the structural parameters and the e nergetics of offretite, when a Si4+ ion is substituted by (Al3+, H+). The calculations have been performed on a periodically repeated unit c ell with 54 atoms and a proton. in agreement with previous cluster cal culations, we conclude that the sites with the lowest (Al, H)/Si subst itution energies are also those with the largest proton affinity. In a ddition a correlation previously reported between acidity and Al-O-Si bond angles is confirmed.