AB-INITIO MOLECULAR-DYNAMICS FOR DETERMINATION OF STRUCTURES OF ALKALI-METAL CLUSTERS AND THEIR TEMPERATURES BEHAVIOR - AN EXAMPLE OF LI-9(+)

It will be shown that an ab initio molecular dynamics procedure based on gradient corrected density functionals for exchange and correlation and using a Gaussian atomic basis (AIMD-GDF) implemented for parallel processing represents a suitable tool for detailed and accurate inves tigation of structural and dynamical properties of small systems. Grad ients of the Born-Oppenheimer ground state energy, obtained by iterati ve solution of the Kohn-Sham equations, are used to calculate the forc es acting on atoms at each instantaneous configuration along trajector ies generated by solving classical equations of motion. Dynamics of di fferent isomers of the Li-9(+) cluster have been investigated as a fun ction of excess energy. It is shown that different isomers, even those similar in energy, can exhibit different structural and dynamical beh avior. The analysis of the simulations leads to the con elusion that s tructures with a central atom, in particular the centered antiprism of Li-9(+) exhibit concerted mobility of the peripheral atoms at relativ ely low excess energy. In contrast, compact tetrahedral type structure s show much more rigid behavior at low excess energy. However, the for mer ones need larger excess of internal energy to undergo isomerizati ons to geometrically different structures than the latter ones. At the time scale of our simulations we found that for the intermediate exce ss energies it is ''easier'' to carry the cluster in the basin of the lowest energy isomer than in the reverse direction. It has been found that the liquid-like behavior in small Li clusters becomes apparent at relatively high temperature in spite of large mobility of their atoms .