Abstract
We present calculations of tunneling splittings in selected small water clusters, based on a recently developed path integral molecular dynamics (PIMD) method. The ground-rotational-state tunneling motions associated with the largest splittings in the water dimer, trimer, and hexamer are considered, and we show that the PIMD predictions are in very good agreement with benchmark quantum and experimental results. As the tunneling spectra are highly sensitive to both the details of the quantum dynamics and the potential energy surface, our calculations are a validation of the MB-Pol surface as well as the accuracy of PIMD. The favorable scaling of PIMD with system size paves the way for calculations of tunneling splittings in large, nonrigid molecular systems with motions that cannot be treated accurately by other methods, such as the semiclassical instanton.
Highlights
The dynamics of water clusters have been the subject of intensive research efforts over the past few decades, due in part to the fundamental importance of water and the presence of water clusters in a number of different environments.[1]
Theoretical efforts in understanding the quantum dynamics of water clusters are hampered by the unfavorable scaling of computational times as a function of system size
Recent efforts involving path integral methods have become promising new avenues for accurately calculating tunneling splittings in ground rotational states, with instanton calculations being straightforward.[15−19] Methods exist for automating the instanton search[20] and substantially improving the computation time required.[21,22]
Summary
The dynamics of water clusters have been the subject of intensive research efforts over the past few decades, due in part to the fundamental importance of water and the presence of water clusters in a number of different environments.[1]. We show that the PIMD method can accurately reproduce the tunneling splittings of these motions, in contrast to the instanton predictions, which exhibit large discrepancies with reference values.
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