Quasi-ab initio dynamics: a test trajectory study of the H+H2 reaction using energies and gradients based on scaling of the external correlation

We have carried out a test dynamics study of the prototype H+H2 exchange reaction by running quasi-classical trajectories `on-the-flyʹ using ab initio correlated energies which have been previously corrected semiempirically by the double many-body expansion plus scaling of the external correlation method to account for size-limitations of the one-electron basis set and configuration interaction expansion. The method is general and gives results in agreement with conventional trajectory calculations carried out on the accurate double many-body expansion potential energy surface for H3.