Structural properties and quantum effects in protonated helium clusters. II. Quantum Monte Carlo calculations for the smaller aggregates

The computed interaction potential energy surface between an He atom and the ionic core unit (HHe₂)⁺, discussed in the preceding paper, is employed here to analyse the structures of the protonated, small clusters of He, and to evaluate the effects of quantum behaviour on the results reached in previous dynamical calculations carried out using ab initio classical dynamics. The method of the present analysis involves numerical solutions of diffusion Monte Carlo (DMC) equations via random walk techniques and allows us to extract global minimum energy configurations for the quantum ground-states of the smaller clusters. The values of the zero point energy, the effect of competitive growth dynamics between various configurations and the evidence for the presence of clear shell structures in the protonated clusters are among the features from the present DMC calculations, which we discuss in this work.