  We present a computational study into the adsorption properties of CO$_2$ on
amorphous and crystalline water surfaces under astrophysically relevant
conditions. Water and carbon dioxide are two of the most dominant species in
the icy mantles of interstellar dust grains and a thorough understanding of
their solid phase interactions at low temperatures is crucial for understanding
the structural evolution of the ices due to thermal segregation. In this paper,
a new H$_2$O-CO$_2$ interaction potential is proposed and used to model the
ballistic deposition of CO$_2$ layers on water ice surfaces, and to study the
individual binding sites at low coverages. Contrary to recent experimental
results, we do not observe CO$_2$ island formation on any type of water
substrate. Additionally, density functional theory calculations are performed
to assess the importance of induced electrostatic interactions.

Astrophysics of Galaxies;Chemical Physics