Calculations of Silicon Self-Interstitial Defects

We report a theoretical study of self-interstitial defects in silicon using local density approximation (LDA), PW91 generalized gradient approximation (GGA), and fixed-node diffusion quantum Monte Carlo (DMC) methods. The formation energies of the stablest interstitial defects are about 3.3 eV within the LDA, 3.8 eV within the PW91-GGA, and 4.9 eV within DMC. The DMC results indicate a value for the formation $+$ migration energy of the self-interstitial contribution to self-diffusion of about 5 eV, which is consistent with the experimental data. This confirms the importance of a proper treatment of electron correlation when studying such systems.