  Crystallization and vitrification of tetrahedral liquids are important both
from a fundamental and a technological point of view. Here, we study via
extensive umbrella sampling Monte Carlo computer simulations the nucleation
barriers for a simple model for tetrahedral patchy particles in the regime
where open tetrahedral crystal structures (namely cubic and hexagonal diamond
and their stacking hybrids) are thermodynamically stable. We show that by
changing the angular bond width, it is possible to move from a glass-forming
model to a readily crystallizing model. From the shape of the barrier we infer
the role of surface tension in the formation of the crystalline clusters.
Studying the trends of the nucleation barriers with the temperature and the
patch width, we are able to identify an optimal value of the patch size that
leads to easy nucleation. Finally, we find that the nucleation barrier is the
same, within our numerical precision, for both diamond crystals and for their
stacking forms.
