Vibrational and rotational bound states in floppy triatomic systems: The distributed Gaussian functions approach

A variational method based on the use of bond coordinates and of a basis set expansion described by distributed Gaussian functions (DGF) is reviewed for its applications to the study of weakly bound triatomic clusters. This approach will be shown to be particularly well suited to treat very diffuse states as those presented by Noble gas (Ng) containing systems like the Ng₃, and Ng₂X, with X being also a very weakly bound atomic impurity. Several statistical properties such as radial distributions, sizes and dominance of triangular configurations for the corresponding bound states are shown to be directly obtained with this method over the whole spectrum of the floppy cluster bound states, in both the rotationless case and also when special care is taken to define rotational constants to yield rovibrational states and their energy levels.