Vacancy cluster in graphite: Migration energy and aggregation mechanism

Abstract

Abstract. Vacancy clusters in graphite have been investigated using Density Functional T heory (DFT) within B3LYP exchange-functional. The smallest size of vacancy clusters (V 4 ) has been chosen to study the migration energy and aggregation mechanism. Two main types of V 4 vacancy clusters have been modeled, the disc ( ) and the line vacancy clusters; including boat vacancy ( ) and zig-zag vacancy ( ). The results show that the presence of unstable V 3 vacancy may induce the mono-vacancy to migrate with low energy and vanish through forming stable V 4 vacancy cluster. Also, the calculated energy barriers required to form the boat vacancy cluster ( ), the zig-zag vacancy cluster ( ) and disk vacancy cluster ( ) support that the disc and the boat vacancy clusters co-exist. However the zig-zag type might only exist by knocking-out mechanism for highly irradiated graphite.