PLATINUM CLUSTERS COLLISIONS WITH SINGLE WALL CARBON NANOTUBES Ana Proykova , Stoyan Pisov, Hristo Iliev Faculty of Physics, University of Sofia, James Bourchier Blvd. 5, 1164 Sofia, Bulgaria E-mail: anap@phys.uni-sofia.bg The carbon nanotubes are usually assumed as perfect species in most of the studies. In practice, even high-quality Single-Wall Carbon Nano Tubes (SWCNTs) contain on average one structural defect per 4 µm [1]. In the present study we compare the perfect (10,0) and (20,0) and defective SWCNTs in collisions with platinum clusters Pt n , n =2, 9, 13 of various kinetic energies (50 - 100 eV/atom) in order to understand the melting and disintegration of small clusters and, also, the hardiness of the SWCNT when imposed upon heavy ion irradiation. Platinum clusters (cationic and anionic) containing up to 24 Pt atoms can be formed by laser vaporization [2] and ion irradiation of SWCNT is feasible in the modern experiments [3]. Thus, computations can be compared with experimental data once available. Molecular dynamics simulations with a mixture of empirical and semi-empirical potentials [4] have been performed to study the result of collisions of Pt clusters with perfect and defective single-walled carbon nanotubes with open ends. Carbon-carbon interactions in the nanotube have been modeled with a semi-empirical potential due to Brenner [5]: E CNT =  i  j<i  V R (r ij ) - ¯ B ij V A (r ij )  (1) Carbon-platinum interactions have been described with the 12-6 Lennard-Jones potential: E C−Pt (r)=4ǫ   σ r  12 -  σ r  6  (2) with σ =2.905 ˚ A and ǫ = 256K . Metallic bonding in the Pt cluster was computed with the n-m Sutton-Chen potential [6] that implemented the basic model of Finnis and Sinclair [7]. For the platinum clusters n=10 / m=8: E Pt N = ǫ  i  1 2  j =i  a r ij  10 - c √ ρ i  ρ i =  j =i  a r ij  8 (3) ρ i is the local density; ǫ = 11605K , a =3.9242 ˚ A and c = 34.408. For the case of initially perfect SWCNTs when Pt 9 clusters hit the tubes perpendicular to their axis, the following results have been obtained. Depending on the tube length (400 C atoms or 3000 C atoms), SWCNT diameter, fixed or free SWCNT ends we observe: (a) short CNTs with fixed ends reflect the clusters; (b) both short and long CNTs generate shock waves and twist in collisions if the ends are free; (c) energetic clusters (above 70 eV/atom) penetrate