INVESTIGATION OF INTERACTION IN C-60 EMBEDDED COMPLEXES (X-AT-C-60) (X EQUALS ALKALI OR HALOGEN) AT A SERIES OF RADIAL POSITIONS BY BUCKINGHAM POTENTIAL FUNCTION

Two typical series of C-60 embedded complexes (X@C-60) (X = Li, Na, K, Rb, Cs; F, Cl, Br, I) have been chosen to study as prototypes, in whi ch the Buckingham potential (exp-6-1) function was applied to calculat ing the interactions of the atom pairs. The potential parameters are o btained from related crystals by the simulations using molecular mecha nics methods. To utilize the symmetry of the potential field in C-60, the calculation is carried out along five typical radial directions. T he computational results show that the interaction between the embedde d atom and the C-60 cage is not purely electrostatic. The repulsive en ergy, E(rep), accounts for from 0.2% to 6.6% (for the alkali series), and from 1.5% to to 58% (for the halogen series); the dispersive energ y E(dis), accounts for from 1.2% to 6.5% (for the alkali series), and from 2.2% to 42% (for the halogen series); and the electrostatic energ y, E(es), accounts for 99% to 87% (for the alkali series) and from 96% to 0% (for the halogen series) when the embedded atom is put at the c enter of the cage. E(rep) reaches up to 8% similar to 35% (alkali), an d 16% similar to 74% (halogen); E(dis) up to 4% similar to 16% (alkali ) and 7% similar to 26% (halogen); and E(es) falls down to about 88% s imilar to 49% (alkali), and 96% similar to 0% (halogen), when the embe dded atom deviates 1.8 Angstrom from the cage center. The total intera ctions, E(inter), are all attractive for X (X = Li, Na, K, Rb, Cs; F, Cl, Br), but repulsive for the I atom. It is shown that the potential field in the C-60 cage has nearly spherical symmetry in an area with a radius of 1.8 Angstrom around the cage center. The same kinds of inte ractions for the atoms in the two individual series are compared, and some variation rules are obtained. For (Li@C-60), the minimum energy e quilibrium point deviates hom the center by about 0.5 Angstrom. (C) 19 96 by John Wiley & Sons, Inc.