  We present a method to include the effects of gravity in the plasma physics
code Cloudy. More precisely, a term is added to the desired gas pressure in
order to enforce hydrostatic equilibrium, accounting for both the self-gravity
of the gas and the presence of an optional external potential. As a test case,
a plane-parallel model of the vertical structure of the Milky Way disk near the
solar neighbourhood is considered. It is shown that the gravitational force
determines the scale height of the disk, and it plays a critical role in
setting its overall chemical composition. However, other variables, such as the
shape of incident continuum and the intensity of the Galactic magnetic field,
strongly affect the predicted structure.
