[GS_C_MS] Preferred States for Coupled Electron-Nuclear Systems
ABSTRACT
In mixed quantum–classical (MQC) methods for electron-nuclear systems, the choice of basis remains an unresolved issue, despite its central role in determining the accuracy and consistency of simulations. Here we propose a natural and efficient basis for electron–nuclear dynamics by drawing on the concepts of pointer and preferred states from decoherence theory, adapted to systems where electrons and nuclei interact strongly. Within this framework, we show that 1) the independent dynamics exploited by MQC methods is best understood as a manifestation of entanglement viewed in a preferred basis, rather than a consequence of decoherence, and 2) the adiabatic Born–Oppenheimer states satisfy the conditions of an approximate preferred basis. This perspective reconciles widely used approximations with a more fundamental structure of the theory—explaining the long-observed success of BO treatments outside strongly nonadiabatic regions— and provides a systematic route to more reliable MQC strategies.
