  The fragility, that controls the temperature-dependent viscous properties of
liquids as the glass transition is approached, in various glass-forming liquids
with different atomic interactions and densities is investigated by molecular
dynamic simulations. We show the landscape of fragility in purely repulsive
systems can be separated into three regions with qualitatively disparate
dynamic behaviors, suggesting that the density plays an unexpected role for
understanding the repulsive steepness dependence of fragility. Furthermore, the
vastly dissimilar influences of attractive interaction on fragility could be
estimated from the structural properties of related zero-temperature glasses
