Here, we quantitatively estimate the impact of the inevitable Si surface passivation prior to III-V/Si heteroepitaxy on the surface energy of the Si initial substrate, and explore its consequences for the description of wetting properties. Density functional theory is used to determine absolute surface energies of P-and Ga-passivated Si surfaces and their dependences with the chemical potential. Especially, we show that, while a ≈90 meV/Å 2 surface energy is usually considered for the nude Si surface, surface passivation by Ga-or P-atoms leads to a strong stabilization of the surface, with a surface energy in the [50-75 meV/Å 2 ] range. The all ab initio analysis of the wetting properties indicate that a complete wetting situation would become possible only if the initial passivated Si surface could be destabilized by at least 15 meV/Å 2 or if the III-V (001) surface could be stabilized by the same amount.