A molecular dynamics study of pristine and doped polyacetylene

Abstract

The molecular dynamics simulation method has been used to study crystalline trans-polyacetylene both in its pristine and in its doped form. No constraints have been included in the simulations, so that both bond lengths and bond angles have been allowed to change. The potential parameters of the interchain and intrachain interactions had been derived by using bond energies, vibrational and structural data. The power spectra of the pristine polymer have been evaluated and they reproduce the main peaks observed in Raman and infrared experimental measure-ments. The trans-polyacetylene system has been doped with lithium and potassium and three different doping levels have been considered. Complete ionization of the alkali metals has been assumed, with charge being transferred to the carbon atoms in the (CH)_x chains in a uniform fashion. For all the densities, the alkali metals follow an oscillatory motion, in which the amplitude decreases as their con-centration increases. Conseauently, their corresponding diffusion coefficients are negligible.