Total energy calculations of the lattice properties of cubic and hexagonal diamond

Using a first-principles method based on density functional theory, we have carried out a study of static properties and vibration frequencies at the (Formula presented) point of cubic and hexagonal diamonds. The bulk modulus and bond length are found to be slightly larger in hexagonal diamond than in cubic diamond. At the (Formula presented) point, there are five Raman active modes with three different frequencies but no IR active mode of hexagonal diamond is found. The Raman active modes of hexagonal diamond contain one nondegenerate mode (Formula presented) and two doubly degenerate modes (Formula presented) and (Formula presented) The calculated frequency of the triply degenerate Raman active mode (1334 (Formula presented) of cubic diamond agrees very well with the experimental value (1333 (Formula presented).