Semiclassical tunneling rates from ab initio molecular dynamics

We demonstrate a new ab initio semiclassical technique for investigating tu nneling effects. Using a semiclassical approach, the method incorporates tu nneling effects into first principles molecular dynamics. We apply the meth od to the intramolecular proton transfer in malonaldehyde and find good agr eement with the experimentally measured tunneling splitting. This agreement suggests a wide applicability of the new method to proton transfer and cou pled electron-proton transfer processes.