Computed positron lifetimes in vacancies and vacancy-iron clusters in gold

Annihilation characteristics are calculated for positrons trapped in clean and impurity decorated vacancy clusters in Au. The positron lifetime depends strongly on the structure of the clusters. In a strongly relaxed vacancy cluster, the lifetime can become smaller than the lifetime in a single vacancy. The substitution of some neighbour atoms of a vacancy cluster by Fe atoms has only a minor effect on the positron lifetimes.