Toward non‐Born–Oppenheimer quantum chemistry

AbstractA practical quantum theory for unifying electronic and nuclear dynamics, which were separated by the Born–Oppenheimer approximation, is proposed. The theory consists of two processes. Nonadiabatic (quantum) electron wavepacket dynamics on branching (non‐Born–Oppenheimer) nuclear paths are first constructed. Since these paths are not the classical trajectories, most of the existing semiclassical theories to generate quantum wavepacket do not work. Therefore, we apply our own developed semiclassical wavepacket theory to these generated non‐Born–Oppenheimer paths. This wavepacket is generated based on what we call the action decomposed function, which does not require the information of the so‐called stability matrix. Thus, the motion of nuclei is also quantized, and consequently the total wavefunction is represented as a series of entanglement between the electronic and nuclear wavepackets. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009