Diffusion Monte Carlo approaches for investigating the structure and vibrational spectra of fluxional systems

摘要

Recent advances in diffusion Monte Carlo (DMC) are reviewed within the context of the vibrational motions of systems that undergo large amplitude motions. Specifically, the authors describe the DMC approach for obtaining the ground state wave function and zero-point energy (ZPE) of the system of interest, as well as extensions to the method for evaluating probability amplitudes, rotational constants, vibrationally excited states and methods for obtaining vibrational spectra. The discussion is framed in terms of the properties of several systems of current experimental and theoretical interest, specifically complexes of neon atoms with OH or SH, H3O2-, H5O2+, and CH5+. The results of the DMC simulations provide the information necessary to characterize the extent of delocalization of the probability amplitudes, even in the ground vibrational states. Methods for evaluating expectation values and vibrationally excited states are explored, and, when possible, the results are compared with those from other approaches. Finally, the methods for evaluating intensities are described and existing and future challenges for the approach are reviewed.