Electronic structure global surfaces

A. Electronic Structure Global Potential Energy Surfaces... 

The nature of the electronic and geometric structure of the surface is usually crucial in determining the reaction rate. The effect of surface morphology will be considered in the next section, but here we will exemplify the effect of global variations in electronic structure by considering a particular catalytic reaction, namely CO hydrogenation, and how the choice of different transition metals affect the selectivity of the product pattern. This is illustrated in fig. 36 and shows that metals in group VIII tend to be the Fischer-Tropsch... 

The difference from classical force field based simulations where the forces are calculated from pre-defined pair potentials is that the forces are derived from the global potential energy surface of an electronic structure theory. The vastly higher computational costs of an electronic structure calculation restrict the system size and the length of trajectories accessible by ab initio molecular dynamics simulations. However, it becomes clear that CPMD and AIMD are important steps towards general predictive methods, due to their independence from parameterizations. 

Recently, Hoffmann and Schatz(7ij have developed a new level of treatment of spin-orbit effects in bimolecular reactions which enables a more sophisticated treatment of intersystem crossing d3mamics than in the past. In this treatment high quality electronic structure n thods are used to determine global surfaces for the reaction and spin-orbit matrix elements, and then trajectory surface hopping (TSH) methods are used to determine properties of the bimolecular collisions such as reactive cross sections and state distribution information. In an application of this theory to the O + H2 reaction, the spin-orbit matrix elements were determined as a function of position, and then TSH calculations were done within a diabatic representation to determine cross sections. Intersystem crossing effects were found to be small for O + H2 due to... 

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