Ground-state geometries and optical properties of Na8-xLix (x=0-8) clusters -: art. no. 053204

We have investigated equilibrium geometries of mixed clusters Na8-xLix (x=0-8) using ab initio molecular dynamics within the framework of density functional theory. The resulting cluster geometries show evolution from C-3v symmetry for Li-8 to D-2d symmetry for Na-8 via T-d symmetry (Li4Na4). We also present and discuss the absorption spectra obtained using the time-dependent local density approximation formalism. The calculated absorption spectra of all Na8-xLix clusters demonstrate the presence of a strong plasmon peak located approximately at the same energy (approximate to2.7 eV). Our calculations predict nearly the same oscillator strengths for the main plasmon peaks of Li-8 and Na-8. Since the polarizabilities of Li-8 (9.7 Angstrom(3)) and Na-8 (14.02 Angstrom(3)) are significantally different, the above observation indicates the significance of nonplasmon contributions in the optical spectrum of Li-8 and implies that the simple jellium approach and the plasmon pole approximation are not valid for Li-8.