Nucleation of a sodium droplet on C-60

We investigate theoretically the progressive coating of C-60 by several sodium atoms. Density functional calculations using a nonlocal functional are performed for NaC60 and Na2C60 in various configurations. These data are used to construct an empirical atomistic model in order to treat larger sizes in a statistical and dynamical context. Fluctuating charges are incorporated to account for charge transfer between sodium and carbon atoms. By performing systematic global optimization in the size range 1less than or equal tonless than or equal to30, we find that NanC60 is homogeneously coated at small sizes, and that a growing droplet is formed above ngreater than or equal to8. The separate effects of single ionization and thermalization are also considered, as well as the changes due to a strong external electric field. The present results are discussed in the light of various experimental data.