A Multiwavelet Treatment of the Quantum Subsystem in Quantum Wavepacket Ab Initio Molecular Dynamics through an Hierarchical Partitioning of Momentum Space.

We present an hierarchical scheme where the propagator in quantum dynamics is represented using a multiwavelet basis. The approach allows for a recursive refinement methodology, where the representation in momentum space can be adaptively improved through additional, decoupled layers of basis functions. The method is developed within the constructs of quantum-wavepacket ab initio molecular dynamics (QWAIMD), which is a quantum-classical method and involves the synergy between a time-dependent quantum wavepacket description and ab initio molecular dynamics. Specifically, the current development is embedded within an "on-the-fly" multireference electronic structural generalization of QWAIMD. The multiwavelet treatment is used to study the dynamics and spectroscopy in a small hydrogen bonded cluster. The results are in agreement with previous calculations and with experiment. The studies also allow an interpretation of the shared proton dynamics as one that can be modeled through the dynamics of dressed states.