Large-scale calculation of optical dielectric functions of diamond nanocrystallites

The real-time real-space higher-order finite-difference method is applied to the calculation of dielectric functions of diamond crystallites. The calculation is performed for cubic grains of various sizes, the largest of which is of 4-nm linear dimension and contains 13 460 carbon atoms. The surface dangling bonds are terminated with hydrogen atoms, and empirical pseudopotentials are used for the two types of atoms. The shift of the absorption peak with the crystallite size is a manifestation of the quantum size effect.