First-principles calculation of intrinsic defect formation volumes in   silicon
  We present an extensive first-principles study of the pressure dependence of the formation enthalpies of all the know vacancy and self-interstitial configurations in silicon, in each charge state from -2 through +2. The neutral vacancy is found to have a formation volume that varies markedly with pressure, leading to a remarkably large negative value (-0.68 atomic volumes) for the zero-pressure formation volume of a Frenkel pair (V + I). The interaction of volume and charge was examined, leading to pressure--Fermi level stability diagrams of the defects. Finally, we quantify the anisotropic nature of the lattice relaxation around the neutral defects. 
Scott A. Centoni, Babak Sadigh, George H. Gilmer, Thomas J. Lenosky,   Tomas Diaz de la Rubia, Charles B. Musgrave