New catalyst design is a grand challenge

Heterogeneous Catalysis Requires Exascale Computing

Mesoporous silica nanoparticles (MSN) are highly effective and selective heterogeneous catalysts for a wide variety of important reactions. Exascale computing is essential to study the catalysis process because of the large number of atoms that must be treated with accurate methods.

MSN selectivity is provided by “gatekeeper” groups (red arrows in Figure) that allow only desired reactants A to enter the pore, keeping undesirable species B from entering the pore. The presence of a solvent further complicates the problem. Accurate electronic structure calculations are needed to deduce the reaction mechanism (s), including the effects of various solvents and to subsequently design even more effective catalysts. The narrow pores (3-5 nm) can create a diffusion problem that can prevent product molecules from exiting the pore. So, in addition to elucidating the reaction mechanism, it is important to study the dynamics of the reaction process, in which a sufficiently realistic cross section of the pore is included. An adequate representation of the MSN pore requires thousands of atoms with a reasonable basis set.

Consider, for example, 5,000 heavy atoms with the aug-cc-pVTZ basis set. This size system amounts to more than 500,000 basis functions, not including the hydrogen atoms, the reacting molecules, and the solvent molecules. An entire system would involve upwards of one million basis functions.

The development of an understanding of the reaction mechanism and the dynamics of the system(s) of interest is well beyond the scope of current hardware and software. A solution to accurate studies of problems in heterogeneous catalysis will require the development of new mathematical and algorithmic approaches that combine high scalability with high accuracy.