ROTATIONAL EXCITATIONS OF QUANTUM LIQUID CLUSTERS - HE-7 AND (H2)7

We have studied the quantum clusters, He-7 and (H-2)7, in their ground (L = 0) and rotationally excited states (L = 2-8 for He and L = 2-12 for H-2) by variational Monte Carlo, and selectively by diffusion Monte Carlo. The optimized trial wave functions are eigenfunctions of L2, and, as such, are orthogonal and yield upper bounds to the energy of each state. We report energies and structural results, including density profiles and moments-of-inertia distributions. Overall, the He-7 cluster is more delocalized than the (H-2)7 Cluster, but the computed structures show that both He-7 and (H-2)7 are highly nonclassical and nonrigid, evolving from spherical to toroidal structures as the angular momentum increases. We find that by L = 2 for He-7 and by L = 6 for (H-2)7, the clusters become metastable with respect to dissociation, as determined by comparison of excited-state energies of the N = 7 clusters with the ground-state energies for N = 6. The root-mean-square bond length fluctuations indicate that both N = 7 clusters are liquidlike in the L = 0 ground state, according to the Lindemann criterion. These fluctuations increase with L, implying a further decrease in rigidity for the rotationally excited states.