CALCULATION OF EDGE AND VERTEX ENERGIES OF DIAMOND MICROCRYSTALS

Preferential crystallographic growth planes are influenced to a large extent by the shape of the microcrystals that nucleate the growth. In contrast with macroscopic crystals, for nanometer scale microcrystals the energies associated with edges and vertices play a crucial role in determining an energetically favourable shape. We present a model for the computation of edge and vertex energies within the framework of s emi-empirical quantum chemical calculations for atomic clusters. For t wo diamond crystallite shapes, both terminated by hydrogen saturated ( 111) surfaces, energy coefficients for the bulk and surface as well as two types of edges and vertices are obtained. The values are consiste nt with measurements. Size dependent effects are investigated by calcu lating the energy per atom for arbitrary sizes of a given shape, from the coefficients. It is found that even for this simple example, there is an energy cross-over at small crystallite size.