First-principles calculations of the bulk modulus of diamond

Abstract

A first-principles pseudopotential approach, which gives an alternative to the stress theorem developed by Nielsen and Martin a few years ago, is proposed to calculate the bulk modulus of solids. The experimental data show that the bulk modulus is approximately correlated to the hardness and consequently is used as a guide in the theoretical predictions of new superhard materials, i.e. materials with hardness close or higher than that of diamond. The value of the bulk modulus can be deduced from those of the elastic constants that are calculated from their analytic expressions established in the framework of the density functional theory. The drawbacks of the previous methods for calculating the elastic coefficients of the solids, i.e. introduction of arbitrary deformations of the unit cell and calculation of stretched physical quantities, are then avoided.