Local interpolation of ab initio potential energy surfaces for direct dynamics studies of chemical reactions

A `directʹ molecular dynamics technique, which calculates the ab initio data points simultaneously within the dynamics simulation is presented. The energies and forces used in quasiclassical trajectory simulations are determined by a least-squares interpolation scheme in rectangular finite elements. The data points are chosen by an automatic selection procedure, which assures that only dynamically relevant parts of the potential energy surface (PES) are interpolated. The energies and gradients at all selected grid points are stored and reused for later trajectories. The efficiency of the method is demonstrated by quasiclassical simulations of scattering experiments on the 3-dimensional PES of the reaction F+H2.