  Three different models of AgI are studied by molecular dynamics simulations.
The first one is the rigid ion model (RIM) with the effective pair potential of
the Vashishta and Rahman form and the parameterization proposed by Shimojo and
Kobayashi. The other two are polarizable ion models in which the induced
polarization effects have been added to the RIM effective pair potential. In
one of them (PIM1) only the anions are assumed to be polarizable by the local
electric field. In the other one (PIM2s) the silver polarization is also
included, and a short-range overlap induced polarization opposes the
electrically induced dipole moments. This short-range polarization is proved to
be necessary to avoid overpolarization when both species are assumed to be
polarizable. The three models reproduce the superionic character of alpha-AgI
at 573 K and the liquid behavior of molten AgI at 923 K. The averaged spatial
distribution of the cations in the alpha-phase obtained for PIM1 appears to be
in better agreement with experimental data analysis. The PIM1 also reproduces
the structure factor prepeak at about 1 reciprocal angstrom observed from
neutron diffraction data of molten AgI. The three models retain in the liquid
phase the superionic character of alpha-AgI as the mobility of the cations is
significantly larger than that for the anions. The ionic conductivity for the
polarizable ion models is in better agreement with experimental data for
alpha-AgI and molten AgI.
