Transition-state lattice modes and the breakdown of adiabatic tunneling for hydrogen and deuterium in bcc Nb
The study investigated how light atoms like hydrogen and deuterium tunnel through defects in bcc Niobium. They found that standard models fail because tunneling is a collective, nonadiabatic process involving strong coupling to lattice vibrations. A five-dimensional Lattice-Renormalized Born-Oppenheimer (LRBO) framework is required to accurately describe the tunnel splittings, showing that the light particle and lattice modes must be treated together.