DENSITY-FUNCTIONAL THEORY STUDY OF SOME STRUCTURAL AND ENERGETIC PROPERTIES OF SMALL LITHIUM CLUSTERS

Some properties of small Li-n clusters (n up to 20) are theoretically investigated, within the density functional theory formalism. The stru ctural properties are examined at the so-called local level of approxi mation. For very small clusters (n less than or equal to 8), the Li-n conformations which are well known from ab initio calculations are fou nd at very low computational cost. For n>8, optimal starting geometrie s are generated from two growth patterns, based on the increase of the number of pentagonal subunits in the clusters by adsorption of one or two Li atoms. Several new stable structures are proposed, for which t he corresponding vibrational analysis is performed for n up to 18. The study of energetic properties and stability requires the use of gradi ent-approximated functionals. Such functionals are used for the determ ination of the relative stability of these clusters. For example, we s how that the icosahedral structure is the most favorable geometry for Li-13, whereas this is not the case for Na-13. Ionization potentials a nd binding energies are also investigated in regard to the size and th e geometry of the clusters. Comparison with experimental results and o ther theoretical approaches (such as nonspherical jellium model) sugge sts that some combinations of gradient-corrected functionals are more adapted than others to describe Li-n energetic and structural properti es. (C) 1996 American Institute of Physics.