  Here, we quantitatively estimate the impact of the inevitable Si surface
passivation prior to III-V/Si hetero-epitaxy 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 dependencies with the
chemical potential. Especially, we show that, while a ~90 meV/$\r{A}^2$ 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/$\r{A}^2$] 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/$\r{A}^2$ or if the III-V (001) surface could be stabilized by the
same amount.
