THE GEOMETRIC STRUCTURES AND OPTICAL-RESPONSE PROPERTIES OF SMALL NANMG CLUSTERS

The influence of an alkaline-earth atom on the structural and electronic properties of alkali metal clusters is reported. In the lowest energy structures of Na5Mg and Na6Mg, the Mg atom takes the place of one of the Na atoms in the topology of the energetically low lying structures of the corresponding Na(n+1) clusters. In the case of Na7Mg and Na8Mg, those structures containing deformed pentagonal bipyramids as subunits (with the Mg atom at the apical position capped by one or two additional Na atoms) are very close in energy to structures in which the Mg atom is located centrally, with larger coordination number. The optically allowed transitions and oscillator strengths for several structures of Na6Mg and Na8Mg clusters calculated using the multiconfigurational linear response method (MCLR) are compared with those obtained from the random phase approximation (RPA). Both methods give rise to similar dominant features, but the inclusion of higher order excitations is found to influence the fine structure of the spectra which might be of importance for comparison with the experimental data. The spectroscopic patterns for both clusters with 8 and 10 valence electrons are strongly dependent on the position of the nuclei. Structures with the Mg atom in the central position give rise to a very different distribution of intense transitions compared to those with Mg atom at the peripheral position.