This thesis is organized as follows:
• In chapter 2, our present understanding of the silicon vacancy and of the self-diffusion process is shortly reviewed.
• In chapter 3 the First Principles Molecular Dynamics method is illustrated and discussed.
• In chapter 4 the method used to compute the vacancy concentration is exposed.
• In chapter 5 the results of calculations of the vacancy concentration and of the vacancy induced self-diffusion are exposed and compared with the available experimental data.
• In the last chapter we present our conclusions.
