THE ELECTRONIC STATES OF LITHIUM ATOMS IN AMMONIA CLUSTERS AND SOLUTION

A new model electron-ammonia pseudopotential parameterized to ab initio quantum chemistry calculations on small lithium ammonia clusters, Li (NH3)n (n = 1,4), is studied in a variety of environments. For Li (NH3)n clusters, n = 16,32,64,128 the valence electron of the lithium is found to exist in a surface state far from the cation which is localized near the center of mass of the cluster. No bulk states were stabilized. Cluster anions (NH3)n- were also studied and the electron centroid-cluster center of mass probability distribution for (NH3)64-calculated using umbrella sampling. In the present model, there is apparently no barrier to the dissociation of the surface states. No bulk states were found. This set of results appears to disagree with experiments which have been interpreted to indicate bulk states for cluster anions and the clusters containing lithium. Bulk properties of both a single excess electron and the lithium atom in solution are also reported. The solvation energy agrees well with experiment but the spectrum of the excess electron remains somewhat blue shifted as in earlier calculations. However, the valence electron of the lithium atom is found to spontaneously dissociate; a proper-ty not reproduced in previous work.