Thermal expansion in small metal clusters and its impact on the electric polarizability

The thermal expansion coefficients of Na-N clusters with 8 less than or equ al to N less than or equal to 40, and Al-7, Al-13(-), and Al-14(-) clusters are obtained from ab initio Born-Oppenheimer local-density-approximation m olecular dynamics. Thermal expansion of small metal clusters is considerabl y larger than that in the bulk and is size dependent. We demonstrate that t he average static electric dipole polarizability of Na clusters depends lin early on the mean interatomic distance and only to a minor extent on the de tailed ionic configuration when the overall shape of the electron density i s enforced by electronic shell effects. Taking thermal expansion into accou nt brings theoretical and experimental polarizabilities into quantitative a greement.