Improvement of Theoretical Algorithm for Prediction of Carbon Nanotubes Catalytical Activity, Based on Quantum Chemical Semi-Empirical Approaches.

We improved our previous theoretical method for prediction of the catalytic activity of porous materials, which is based on the concept of transition state shape selectivity. This method used adsorption energy calculations for transition state (TS) with «frozen» (only the placement of TS inside the pore is optimized) structure on porous materials with molecular mechanics (MM) as a calculational method. Our improvement consists of application of semi-empirical methods with dispersion correction (e.g., PM3-D3 or PM6-D3H4) instead of MM. We found that with semi-empirical methods adsorption energy dependences on pore diameter are similar to dependences obtained by MM, and also semi-empirical methods predict the same value of the cavity diameter, at which there is a maximum of TS adsorption energy. Despite these similarities in obtained results, semi-empirical methods have the advantages that they can more accurately describe structures, intermolecular interactions and energy values. We have shown that the level of theory (PM3-D3 or RI-MP2/ma-def2-SVP) used for TS structure search, in the case of suggested method, has little effect. [ABSTRACT FROM AUTHOR]