Molecular Dynamics Simulations of Formation of Metal-Containing Fullerene.

Abstract

The growth process of metal-containing fullerene was studied using the molecular dynamics method. As for metalcontaining fullerene, only the metal atoms such as La, Y or Sc are experimentally assigned to be contained inside the carbon cage. In this paper, the difference of growth process and structures of metal-attached carbon clusters were examined using lanthanum and nickel as the additional metal atoms to clarify the effect of the metal atoms. In order to model the potential function between carbon and metal atoms appropriate for the classical MD simulation, the binding energy and charge state of various forms of small clusters MCn (M: La,Ni; n =1-3) were calculated with the density functional theory. A multi-body potential function was constructed as a function of coordinate number of a scandium atom. Here, the Coulomb term and the Morse-type term were separately described considering the large charge transfer from a lanthanum atom to carbon atoms. By using the potential function, the clustering process starting from 500 isolated carbon atoms and 5 metal atoms in a 342 A cubic cell was simulated under the controlled temperature condition at Tc = 3000 K, and the growth history of metal-attached clusters was studied in detail. Figure A-1 shows the growth process of La attached clusters obtained in the simulation. The fan-type structure and mono-cyclic or bi-cyclic rings were reproduced around the metal atom for LaCn (n<20). An open cap structure surrounding the La atom was formed for LaCn (20<n<50) due to the strong Coulomb interaction, and that resulted in the lanthanum-containing caged cluster. When Ni atoms were applied as shown in Figure A-2, the structures of small clusters up to NiC n (n<20) were similar to LaCn (n<20), while tangled-poly-cyclic structures and random cage were dominant for NiCn (20<n<50). The nickel atom attached on one face of the caged structure, and could not stay stably inside the carbon cage structure.