High-resolution spectroscopy experiments performed on weakly-bound clusters are often produced by adiabatic expansion. The resulting clusters have very low temperatures, and, consequently, the behavior of these systems is determined by their low-energy quantum states.

Conventional variational, normal mode, and basis set methods to treat molecular vibrations fail for most clusters because of their strong anharmonicity and floppiness. Quantum Monte Carlo methods, such as diffusion Monte Carlo and its variants, seem to be the only tools available for the computation of properties of excited vibrational states of weakly-bound clusters without uncontrolled approximations.

A panel discussion at a conference at Schloss Ringberg, Germany, in 1997 identified the study of bound states of small 4-He clusters as an important unsolved problem in cluster physics. From this perspective, I shall discuss progress in the computation, as a function of the de Boer parameter, of ground and excited state energies of bosonic van der Waals clusters by means of a correlation function Monte Carlo approach using optimized trial wave functions.

Professor Nightingale is a regular member of the URI faculty. If you'd like to meet with him, please feel free to contact him directly.