  Ab-initio dynamical simulation is used to study the liquid Ga-Se system at
the three concentrations Ga$_2$Se, GaSe and Ga$_2$Se$_3$ at the temperature
1300~K. The simulations are based on the density functional pseudopotential
technique, with the system maintained on the Born-Oppenheimer surface by
conjugate gradients minimization. We present results for the partial structure
factors and radial distribution functions, which reveal how the liquid
structure depends on the composition. Our calculations of the electrical
conductivity $\sigma$ using the Kubo-Greenwood approximation show that $\sigma$
depends very strongly on the composition. We show how this variation of
$\sigma$ is related to the calculated electronic density of states. Comparisons
with recent experimental determinations of the structure and conductivity are
also presented.
