Variational Transition State Theory with Multidimensional Tunneling

This review describes the application of variational transition state theory (VTST) to the calculation of chemical reaction rates. In 1985 two of us, together with Alan D. Isaacson, wrote a book chapter on this subject entitled “Generalized Transition State Theory” for the multi-volume series entitled Theory of Chemical Reaction Dynamics.1 Since that time, variational transition state theory has undergone important improvements due mainly to the ability of this theory to adapt to more challenging problems. For instance, the 1985 chapter mainly describes the application of VTST to bimolecular reactions involving 3–6 atoms, which were the state-of-the-art at that moment. The study of those reactions by VTST dynamics depended on the construction of an analytical potential energy surface (PES). Nowadays, thanks to the development of more efficient algorithms and more powerful computers, the situation is completely different, and most rate calculations are based on “on the fly” electronic structure calculations, which together with hybrid approaches, like combined quantum mechanical molecular mechanical methods (QM/MM), allow researchers to apply VTST to systems with hundreds or even tens of thousands of atoms. Three other major advances since 1985 are that transition state dividing surfaces can now be defined much more realistically, more accurate methodsmore » have been developed to include multidimensional quantum mechanical tunneling into VTST, and the theory has also been extended to reactions in condensed phases.« less