  We have investigated self-bound binary ultra dilute bosonic mixtures at zero
temperature within Density Functional Theory using a Local Density
Approximation. We provide the explicit expression of the Lee-Huang-Yang
correction in the general case of heteronuclear mixtures, and investigate the
general thermodynamic conditions which lead to the formation of self-bound
systems. We have determined the conditions for stability against the
evaporation of one component, as well as the mechanical and diffusive spinodal
lines. We have also calculated the surface tension of the self-bound state as a
function of the inter-species interaction strength. We find that relatively
modest changes of the latter result in order-of-magnitude changes in the
calculated surface tension. We suggest experimental realizations which might
display the metastability and phase separation of the mixture when entering
regions of the phase diagram characterized by negative pressures. Finally, we
show that these droplets may sustain stable vortex and vortex dimers.
