Bulk properties of alkali doped C_(60) solids

摘要

Model calculations are presented for potassium, rubidium and Cesium doped C_(60) solids formed by exohedral doping in pure C_(60) solid. The molecular formula is M_nC_(60), M is the alkali metal (K, Rb and Cs) and n takes integer values 1, 3, 4 and 6. In this work, the C_(60)molecule is modelled as a uniforma spherical shell having surface density of carbon atoms. Part of the electrons released by ionized alkali atoms are distributed on the C_(60) molecule making it an anion, while the rest(say x) are assumed to form a delocalised electron gas. This electron gas screens the Coulomb interaction between the various anion and cations. With these assumptions, the total cohesive energy is calculated taking into consideration van der Waals and screened Coulomb interaction between differenct ions. We found that total charge transfer from cation to anion is favoured. Thus ionic character of alkali doped C_(60) solid is established on the basis of the model. The lattice constant, cohesive energy and Bulk modulus for these systems are in good agreement with other calculation or experimental observations. We make some remarks on phase stability of these solids.