Elastic properties of TiB2 and MgB2

We study the elastic properties, electronic structure and equation of state of titanium diboride and magnesium diboride using a first-principles pseud opotential method. We show that the results of the calculations carried out using the gradient-corrected approximation of the density-functional theor y are in excellent agreement with the most recent experimental data. These results confirm that early reports of anomalously high elastic anisotropy o f TiB2 were based on erroneous experimental data for the off-diagonal compo nents of the elastic coefficients tenser. Present results for TiB2 are more accurate than previously reported Hartree-Fock calculations. Predicted ela stic properties of the recently discovered superconductor, MgB2, are presen ted and compared to contradictory experimental estimates of bulk and linear compressibilities.