Contribution of quantum and thermal fluctuations to the elastic moduli and dielectric constants of covalent semiconductors

Using the density-functional perturbation theory, ab initio calculations have been performed for the contribution of quantum fluctuations to the bulk modulus of diamond, the dielectric constant of diamond, silicon, and germanium, and for the temperature dependence of these quantities. With these data, predictions are made for the bulk modulus and refractive index of isotopically enriched crystals. Where available, experimental data are in good agreement with our results. {} 1996 The American Physical Society.