  We present a wide grid of models for the structure and transmission
properties of warm absorbers in active galactic nuclei (AGN). Contrary to
commonly used constant density models, our absorbing cloud is assumed to be
under constant total (gas plus radiation) pressure. This assumption implies the
coexistence of material at different temperatures and ionization states, which
is a natural consequence of pressure and thermal equilibrium. Our
photoionization code allows us to compute the profiles of the density, the
temperature, the gas pressure, the radiation pressure and the ionization state
across the cloud, and to calculate the radiative transfer of continuum and
lines including Compton scattering. Therefore, equivalent widths of both
saturated and unsaturated lines are properly modeled. For each pair of the
incident spectrum slope and the ionization parameter at the cloud surface there
is a natural upper limit to the total column densities of the cloud due to
thermal instabilities. These maximum values are comparable to the observational
constraints on the column density of warm absorbers which may give support to
constant total pressure models. In all models we note considerable absorption
around 6.4 keV which modifies the intrinsic relativistically broadened iron
line profile originating in an accretion disk illuminated atmosphere. Our
models can be applied to fitting the spectroscopic data from the {\it
XMM-Newton} and {\it Chandra} satellites.
