Ab Initio Molecular Dynamics Calculations to Study Catalysis

The modern versions of the density functional theory (DFT), especially those using the generalized gradient approximation (GGA), have reached (almost) chemical accuracy and thus can be applied to study problems of real chemical interest such as catalysis. The important equations for the DFT, the local density approximation (LDA) and GGA are given. The full-potential linearized augmented plane wave method (LAPW) is used to check the accuracy of GGA in solids. The basic concepts of the ab-initio molecular dynamics (MD) method by Car and Parrinello and its recent implementation using the Projector Augmented Wave (PAW) method which use a similar augmentation as LAPW are described. PAW applications to ferrocene and beryllocene are summarized, which illustrate that vibrational or fluxional behavior are well described. Sodalite, an aluminosilicate, is discussed as a generic zeolite in comparison with gmelinite. A study of the dynamics of such a system allows the determination of e.g., the proton stretch vibrations which can be related to infrared spectra. This is illustrated for the OH stretch vibration of the acid site in silicon-rich sodalite. With this methodology we are able to study the interaction of methanol trapped inside the cage structure of silicon-rich sodalite and to gain new insight into crucial steps of catalytic reactions, namely the hydrogen-bonding and the possible protonation in this system, or a proton exchange reaction. The strategies for parallelizing the PAW code are outlined.